Invest New Drugs DOI 10.1007/s10637-016-0330-2

REVIEW

Targeted therapies in gastric cancer treatment: where we are and where we are going Gianluca Tomasello 1 & Michele Ghidini 1 & Wanda Liguigli 1 & Margherita Ratti 1 & Laura Toppo 1 & Rodolfo Passalacqua 1

Received: 14 December 2015 / Accepted: 9 February 2016 # Springer Science+Business Media New York 2016

Summary Gastric cancer (GC) is one of the most common malignancies and a major cause of cancer-related deaths worldwide. Its incidence has significantly declined over the last few decades, probably due to the identification of specific etiologic agents such as Helicobacter pylori and other dietary and environmental risk factors. Nevertheless, most of the cases are unfortunately diagnosed at an advanced stage justifying median overall survival rates frequently not exceeding one year. Palliative combination chemotherapy usually represented by a platinum-based doublet is the mainstay of treatment in the metastatic setting. Adding a third drug such as an anthracycline or a taxane has been shown to improve response rate and provide limited survival benefits in fit selected patients. Unlike other tumors, the introduction of molecularly targeted drugs in the medical armamentarium for GC is relatively recent with trastuzumab and ultimately ramucirumab constituting the only agents approved to date. Recent advances in the understanding of GC biology have led to the development of novel targeted therapies holding the promise to further improve treatment outcomes. The aim of this paper is to review the main available data coming from clinical trials of targeted drugs and to describe some of the most interesting molecules in clinical development in GC. These include drugs targeting EGFR, angiogenesis, cMET, FGFR2, mTOR and immune checkpoints.

* Gianluca Tomasello [email protected]

1

Oncology Division, Azienda Socio Sanitaria Territoriale di Cremona, Ospedale di Cremona, Viale Concordia 1, 26100 Cremona, Italy

Keywords Gastric cancer . Targeted therapies . Metastatic . Trastuzumab . Ramucirumab

Introduction According to the GLOBOCAN database, almost one million new cases of stomach cancer were estimated to have been diagnosed in 2012, making it the fifth most common malignancy in the world [1]. Gastric cancer (GC) ranks third amongst leading causes of cancer death in both sexes worldwide; accounting for 723,000 deaths: 8.8 % of the total [2]. Incidence varies within different geographic areas. The highest rates are registered in Eastern Asia, Eastern Europe and South America, while the lowest are found in North America and Africa [2]. Over 70 % of GCs occur in less developed countries with a clear predilection for male sex. Despite a remarkable incidence decline worldwide over the last few decades, GC still represents a highly lethal disease, with five-year overall survival (OS) rates for all stages combined generally below 30 % [2]. This is probably due to the significant percentage of metastatic cases at presentation as well as to the aggressive biology. In the advanced setting, a number of meta-analyses have clearly demonstrated the survival benefit associated with chemotherapy compared with supportive care alone and the superiority of combination chemotherapy over therapy with 5FU single agent [3, 4]. Chemotherapy combinations consisting of platinum-based doublets are widely accepted as standard regimens for first-line treatment. In randomized phase 3 trials, adding a third drug (i.e. epirubicin or docetaxel) to the Cisplatin-5FU backbone resulted in only modest OS gains at the cost of significant toxicity and the need for a central venous line [4, 5].

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In 2010, the publication of the results of the pivotal phase 3 TOGA trial finally ushered GC into a new era. Similar to what has been obtained in breast cancer, trastuzumab, an antibody directed anti human epidermal growth factor receptor 2 (HER2), for the first time was shown to significantly prolong survival of HER2-positive metastatic GC patients (approximately 20 % of all esophagogastric [EG] adenocarcinomas) when combined with chemotherapy [6]. This represented a major therapeutic breakthrough and paved the way for a number of clinical trials testing targeted therapies alone or in combination with chemotherapy producing conflicting results. Since then, many research efforts have been made to introduce further biological agents in clinical practice but very few of them were able to reach advanced phases of development. While reviewing the main findings from available clinical trials, this article will discuss the current options involving molecularly targeted therapies in GC treatment and their potential future impact.

Targeting HER2 HER2 is a transmembrane tyrosine kinase receptor characterized by an extracellular ligand-binding domain, an intracellular part with kinase activity and a short transmembrane domain [7]. HER2 protein, encoded by a gene located on chromosome 17q21, belongs to the epidermal growth factor receptor (EGFR) family [7]. Unlike HER-1, HER-3 and HER-4, members of the same family activated by specific molecules, ligand to HER2 remains unknown to date. HER2 is involved in cell proliferation, differentiation, motility and apoptosis [7]. Receptor deregulation or overexpression leads to inappropriate activation of downstream signaling pathways, including members of MAPK and phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) [8]. Approximately 7 to 22 % of EG adenocarcinomas overexpress HER2 [9]. HER2 positivity is more frequently described in intestinal-type than in diffuse type GCs (32 vs 6 %), with high concordance between HER2 status detected on the primary tumor and metastatic sites [10]. Prognostic significance of HER2 status in GC is still a matter of debate [10]. In a clinical setting, the expression of HER2 is initially determined using immunohistochemistry (IHC) [11]. In case of an IHC score of 3+, the patient is eligible for treatment with trastuzumab and chemotherapy. When 2+, the patient should be retested with in situ hybridization (ISH). As a consequence, only ISH-positive cases are suitable for treatment with trastuzumab. An IHC score of 1+ should be considered negative [11]. Trastuzumab Trastuzumab was approved by the Food and Drug Administration (FDA) in October 2010 in combination with

platin/fluoroprimidine-based chemotherapy for the treatment of patients with HER2 overexpressing previously untreated metastatic gastric or gastroesophageal junction (GEJ) adenocarcinoma [12]. Trastuzumab is a fully humanized monoclonal antibody which binds to the extracellular domain of the receptor, thus preventing receptor dimerization, activation of HER2-related signaling and inducing antibody-dependent cellular cytotoxicity (ADCC) [13]. The benefit of adding trastuzumab to conventional chemotherapy was demonstrated in the phase III multicentre international TOGA trial, that compared standard chemotherapy (cisplatin + either infusional 5FU or capecitabine) with or without trastuzumab in patients with advanced HER2-positive adenocarcinoma of the stomach or GEJ [6]. The median overall survival (OS, primary endpoint) was significantly improved in trastuzumab combination arm (13.8 vs 11.1 months; p = 0.0046) [6]. Trastuzumab was also shown to significantly prolong median progression free survival (PFS) (6.7 vs 5.5 months) and radiological response rate (47 % vs 35 %) [6]. Also noteworthy: a post-hoc exploratory analysis showed that treatment with trastuzumab was associated with an even longer survival rate (16.0 months) in patients with high levels (IHC 2+ and FISH positive or IHC 3+) compared with those with low levels (IHC 0 and FISH positive or IHC 1+ and FISH positive) of HER2 protein in their tumors [6]. Furthermore, a treatment effect could not be excluded in any of the predefined subgroups, but was more evident in patients with intestinal GC type [6]. Based upon these data, trastuzumab combined with platin/ fluoropyrimidine-based chemotherapy became the standard of care for metastatic HER2 positive GEJ/GC. Three recent phase II studies evaluated the role of trastuzumab in addition to different polychemotherapies. In particular, the combination of trastuzumab (8 mg/m2 for first cycle and 6 mg/m2 for subsequent cycles on day 1), capecitabine (1000 mg/m2 twice daily on days 1–14) and oxaliplatin (130 mg/m2 on day 1) every three weeks reached a median PFS value of 9.8 months (95 % CI = 7.0–12.6) and a median OS of 21 months (95 % CI = 6.4–35.7) with an objective response rate (RR) of 67 % (95% CI = 54–80 %) [14]. A similar RR (68 %, 95 % CI = 54–80) was obtained by combining trastuzumab with cisplatin and the oral fluoropirimidine S-1 [15]. Median PFS was 7.8 months (95 % CI = 6.0–8.8 months) with a median OS of 16 months (95 % CI = 13.3–not applicable) [15]. Furthermore, the addition of docetaxel (50 mg/m2) to cisplatin (60 mg/m2), S-1 (80 mg per day) and trastuzumab resulted in an impressive response rate of 93.8 % with both median PFS and OS not reached during a median follow-up time of 18.3 months [16]. At present, research in metastatic setting is also focusing on testing different chemotherapy combinations [17] or exploring the utility of maintenance therapy with trastuzumab. Specifically, the HELOISE trial (a study of herceptin in combination with cisplatin/capecitabine chemotherapy in patients

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with HER2-positive metastatic gastric or GEJ cancer) is currently recruiting patients to evaluate whether a higher trastuzumab maintenance dose (loading dose of 8 mg/kg followed by 10 vs 6 mg/kg maintenance doses given every 3 weeks) may translate in better survival outcomes [18]. Additional ongoing trials are evaluating trastuzumab in the perioperative setting. Among these, Her-FLOT is a multicenter phase II study, testing the efficacy and toxicity of trastuzumab in the perioperative therapy of locally advanced HER2 positive GEJ/GC (24-h 5FU 2600 mg/m2, leucovorin 200 mg/m2, oxaliplatin 85 mg/mg2, docetaxel 50 mg/m2, trastuzumab 6 mg/kg then 4 mg/kg d1, repeated every second week for four cycles pre- and postoperatively followed by 9 cycles of trastuzumab monotherapy 6 mg/kg 3weekly) [19]. Preliminary data on pathological complete remission (pCR) rate is promising with >20 % achieving pCR [19]. T-DM1 Trastuzumab emtansine (T-DM1) is an antibody–drug conjugate composed of trastuzumab and DM1, a microtubule polymerization inhibitor. After internalization of the receptor HER2–T-DM1 complex, release of DM1-containing moieties from T-DM1 results in the inhibition of cell division, leading to cell death [20]. Following the positive findings reported in the phase III EMILIA trial, FDA and European Medicines Agency (EMA) approved T-DM1 for treatment of HER2positive breast cancer patients already treated with trastuzumab and a taxane [21]. NCT01641939 is a trial currently recruiting HER2-positive GC patients in second-line setting [22]. This multicenter, randomized, phase II/III study aims at exploring the efficacy and safety of trastuzumab emtansine compared to standard treatment with taxanes (paclitaxel or docetaxel according to physician’s choice) [22]. Positive results from this trial could definitely unfold interesting therapeutic scenarios. Pertuzumab Pertuzumab is a humanized monoclonal antibody binding to a different epitope of HER2 receptor (extracellular dimerization domain II) resulting in a synergistic and complementary activity when combined with trastuzumab [23]. Their association proved to be very effective in breast cancer and, based on the findings of the CLEOPATRA study, pertuzumab was approved in combination with trastuzumab and docetaxel for first-line treatment of metastatic HER2-positive breast cancer [24]. Following this unprecedented median OS benefit (approximately 15 months of difference with the control arm) observed in breast disease, the addition of pertuzumab to trastuzumab plus chemotherapy is being tested in GC in the ongoing JACOB phase III randomized trial [25]. The study

was designed to evaluate the efficacy and safety of pertuzumab added to trastuzumab and chemotherapy in 780 patients with HER2 positive advanced gastric/GEJ cancer. Its results are eagerly awaited [25]. Lapatinib Lapatinib is a small-molecule tyrosine kinase inhibitor (TKI) that targets EGFR1 and HER2 at the same time. Unlike trastuzumab, lapatinib binds to the intracellular domain of the tyrosine kinase receptor [26]. Its activity results in a complete blockade of the receptor autophosphorylation, interrupting the downstream cascade of events [26]. Lapatinib showed synergistic activity with trastuzumab, leading to cell cycle arrest and cell death, and restoring trastuzumab sensitivity in preclinical models [26]. Lapatinib is approved in combination with capecitabine, trastuzumab or anti hormonal therapy in metastatic HER2-positive breast cancer [27–29]. Based upon positive results observed in breast disease [27–29], the logical consequence was to test lapatinib in HER2-positive GC. The TRIO-013/LOGiC trial was a randomized, double blind phase III study evaluating the efficacy and safety of lapatinib in combination with capecitabine plus oxaliplatin (CapeOx) in HER2-positive advanced or metastatic gastric, esophageal, or GEJ adenocarcinoma [30]. Unfortunately, the combination of lapatinib with chemotherapy was not associated with a significant OS improvement (12.2 vs. 10.5 months, HR = 0.91, 95 % CI 0.73-1.12) compared with chemotherapy alone. In subgroup analysis, only Asian patients and those under 60 years gained better results from lapatinib [30]. Another recent phase III trial, TyTAN study, was conducted on an Asian population to test the combination of lapatinib with weekly paclitaxel versus weekly paclitaxel alone in the second-line treatment of HER2-amplified advanced GC [31]. No significant improvement of median OS was registered in the lapatinib plus paclitaxel group compared with paclitaxel alone. However, in subgroup analysis, patients with IHC3+ showed a remarkable 6.5 months advantage in median survival if treated with lapatinib [31].

Targeting EGFR EGFR belongs to ERBb family, a group of transmembrane tyrosine kinases-receptors regulating many different cellular activities like proliferation, survival, migration and differentiation [32]. This family is composed of four receptors: the epidermal growth factor itself (EGFR/ErbB1/HER1), ErbB2 (HER2/neu), ErbB3 (HER3) and ErbB4 (HER4) [32]. EGFR is normally expressed in human tissues and its overexpression or deregulation has been found in a variety of tumors [32]. EGFR overexpression is present in 30–50 % of gastric and

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esophageal cancers [33, 34], making it an ideal target for precise therapeutic strategies. A high correlation between EGFR overexpression and advanced stages and poor prognosis has also been reported in GC patients [35]. Anti-EGFR antibodies Cetuximab (known also as IMC-225 or C225, Erbitux®) is an immunoglobulin G1 chimeric mouse–human monoclonal antibody that binds to the extracellular domain of EGFR, blocking the interaction between the endogenous ligand and the domain itself, enhancing receptor internalization and degradation [36]. Cetuximab was first approved in 2004 in combination with chemotherapy and as a single agent for treatment of patients with EGFR-expressing metastatic colorectal cancer [37]. Favorable results in terms of efficacy and safety were obtained in preclinical and phase II studies testing cetuximab in combination with chemotherapy in advanced GEJ cancer [38–40]. Based on these positive data, a large randomized phase III trial (EXPAND) was designed to compare the addition of cetuximab to capecitabine and cisplatin vs chemotherapy alone in the first-line setting for patients with locally advanced unresectable or metastatic adenocarcinoma of the stomach or GEJ. PFS was the primary endpoint [41]. The addition of cetuximab provided no significant benefit in terms of PFS (4.4 months with cetuximab vs 5.6 months with chemotherapy alone, HR 1.09 [95 % CI 0.92-1.19; p = 0.32] ), OS (9.4 months with cetuximab vs 10.7 with chemotherapy alone, respectively; p = 0.95) and overall response rate (ORR) (30 % vs 29 %, p = 0.77) [41]. Panitumumab (ABX-EGF, Vectibix®) is a fully human immunoglobulin G2 monoclonal antibody that inhibits the binding of both EGF and TGF-alpha to EGFR, blocking the activation of the downstream pathways [42]. FDA approved panitumumab for treatment of EGFR-expressing metastatic colorectal cancer showing progression of disease after therapy with fluoropyrimidine, oxaliplatin, and irinotecan [43]. The randomized, open-label phase III REAL3 trial enrolled patients with untreated, metastatic or locally advanced EG adenocarcinoma to receive EOC (epirubicin, oxaliplatin, capecitabine) or modified-dose EOC associated with panitumumab [44]. Median OS in 275 patients receiving EOC was 11.3 months compared with 8.8 months in 278 patients receiving mEOC + panitumumab (HR 1.37, 95 % CI 1.07-1.76; p = 0.013) suggesting a potential detrimental effect of panitumumab in this particular setting. Moreover, mEOC arm was associated with higher incidence of some G3-4 adverse events such as diarrhea, skin rash and hypomagnesemia [44]. Possible explanations to these disappointing results might be the increased toxicity, which limited the delivery of an adequate dose intensity in the experimental arm and a possible negative interaction of

panitumumab with one or more EOC components (i.e. oxaliplatin). Based on these findings, chemotherapy and panitumumab cannot be recommended for use in an unselected population with advanced EG adenocarcinoma. EGFR does not currently represent an optimal druggable target for EG cancer patients. Identification of strong and reliable predictive biomarkers is definitely needed.

Targeting angiogenesis Over the last few years, several studies have been conducted in metastatic GC testing monoclonal antibodies and smallmolecule TKIs directed against the vascular endothelial growth factor (VEGF) or its receptors, as single agents or in combination with chem otherapy [45, 46]. Carcinogenesis and metastatic processes are mediated by angiogenesis, with VEGF playing a key role [47]. The VEGF family includes VEGF-A, −B, −C, −D and –E and placental growth factor (PIGF). VEGF-A binds to VEGFR-1 and −2, while VEGF-B and PIGF bind to VEGFR-1, and VEGF-C and –D bind to VEGFR-2 and 3 [47]. The activation of these receptors leads to an increase in vascular permeability, endothelial cell proliferation and new blood vessels formation [47]. A number of evidence has been accumulated so far, clearly showing that more aggressive GCs and an increased relapse rate are often associated with an altered or abnormal expression of tumor angiogenesis-related factors [48]. Particularly, VEGF-A and VEGF-D overexpression seem to be related to poor prognosis and resistance to chemotherapy [49]. Antiangiogenic therapies currently being evaluated in GC include: bevacizumab and aflibercept that act locking the VEGFR ligands, ramucirumab that binds the VEGFR and finally sunitinib, sorafenib and novel VEGFR-TKIs [50]. Bevacizumab Bevacizumab is a recombinant humanized monoclonal antibody that targets VEGF-A. Early phase II studies in first-line advanced GC evaluated bevacizumab plus chemotherapy doublets. Bevacizumab (15 mg/kg on day 1) was associated with irinotecan (65 mg/m2) and cisplatin (30 mg/m2) on days 1 and 8 and every 21 days, showing an ORR of 65 % (95 % CI, 46 % to 80 %) and a median survival of 12.3 months (95 % CI, 11.3 to 17.2 months) in 47 patients [51]. An additional small phase II study tested bevacizumab at 7.5 mg/kg plus docetaxel at 70 mg/m2 and oxaliplatin at 75 mg/m2 on day 1 of a 21-day cycle in 38 patients. Median PFS was 6.6 months (95 % CI, 4.4–10.5) and median survival 11.1 months (95 % CI 8.2-15.3) with an ORR of 42 % [52]. The association with three drugs, specifically docetaxel, fluorouracil and cisplatin was explored in an interesting phase II trial involving 44 participants [53]. Researchers from Memorial Sloan Kettering

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Cancer Center reported an impressively long median survival (16.8 months - 95 % CI, 12.1 to 26.1) and an ORR of 67 % (95 % CI, 50 % to 81 %). Unfortunately, such promising results were not replicated in large confirmatory phase III studies. In fact, the AVAGAST trial, randomized over 700 patients to receive bevacizumab 7.5 mg/kg or placebo followed by cisplatin 80 mg/m2 on day 1 plus capecitabine 1000 mg/m2 twice daily for 14 days every 3 weeks [54]. Despite the superiority of the group with bevacizumab in terms of response rate (46 % vs 37.4 %) and PFS (6.7 vs 5.3 months), the study failed to show a significant improvement in median survival (12.1 vs 10.1 months, p = 0.1002) [54]. Interestingly, in the preplanned subgroup analysis, there was the suggestion of an influence of geographic differences in the response to bevacizumab, which appeared to give better results in the American and European patients than in the Asian. Specifically, western patients with diffuse and distal non diffuse-type tumors appeared to benefit most from bevacizumab (OS 11.4 months in the bevacizumab arm vs 7.3 months in the placebo arm) [54]. Finally, differences in median OS in the control arm according to the different continent of origin, were also observed (12.1 months in Asia; 8.6 months in Europe; 6.8 months in Pan-America) [54]. Translational analyses subsequently performed demonstrated in non-Asian patients only trends towards improved OS for subjects with higher baseline plasma VEGF-A levels (HR 0.72) and low basal expression of Neuropilin-1 (HR 0.75) [55]. In all of the above-mentioned phase II and III studies, no signals of new and unexpected adverse events were noticed and most frequent bevacizumab-related toxicities included: hypertension, bleeding, gastrointestinal perforation and thromboembolic events in variable rates [51–55].

Ramucirumab Ramucirumab is a fully human IgG1 monoclonal antibody directed against the extracellular domain of VEGFR-2 [56]. In late 2014, the publication of the definitive results of the pivotal REGARD trial represented a key event in the history of metastatic GC treatment. For the first time a survival benefit provided by an antiangiogenic drug was demonstrated in patients with advanced gastric or GEJ adenocarcinoma progressing after first-line chemotherapy containing platinum and/or a fluoropyrimidine [57]. In this study, patients were randomized in a 2:1 ratio to receive the best supportive care plus either ramucirumab 8 mg/kg or placebo, intravenously once every 2 weeks [57]. Randomization was stratified by weight loss, geographic region and location of primary tumor. Antibody monotherapy managed to increase by 22 % the median survival (HR 0.78; 95 % CI 0.60 to 0.99; p = 0.04) and over 50 % the PFS (HR 0.48; 95 % CI 0.37 to 0.62;

p < 0.0001) [57]. Specifically, median OS and PFS were 5.2 and 2.1 months respectively in patients receiving ramucirumab compared with 3.8 and 1.3 months in patients receiving placebo [57]. Disease control rate was also significantly improved (49 % versus 23 %; p < 0.001) with an acceptable toxicity profile, which was consistent with safety of other agents of the same class (e.g. bevacizumab) [57]. In the phase III, randomized, placebo-controlled RAINBOW study ramucirumab was tested as second-line treatment in combination with paclitaxel [58]. Results were equally positive with all the major endpoints reaching the level of significance in favor of the experimental arm. The response rate was almost double in the group treated with ramucirumab compared with the control group (28 % vs 16 %; p = 0.0001) [58]. The median OS (9.63 months vs 7.36 months; HR = 0.807, 95 % CI 0.678 to 0.962) and PFS (4.4 months vs 2.86 months; HR = 0.635, 95 % CI 0.536 to 0.752) were significantly prolonged with the monoclonal antibody [58]. More frequently reported grade 3 or higher adverse events in the ramucirumab group included neutropenia, hypertension and fatigue, although the rate of febrile neutropenia between treatment arms was similar [58]. However, when ramucirumab was associated with FOLFOX in a randomized double-blinded, multicenter phase II trial in first-line metastatic GC, results were surprisingly disappointing [59]. Despite a better disease control rate (85 % vs 67 %) in favor of the group treated with the VEGFR-2 inhibitor, the intention-to-treat analysis showed no difference in terms of PFS (6.44 vs. 6.74 months) and OS (11.7 vs 11.5 months) [59]. In the attempt to find possible factors contributing to ramucirumab treatment refining and optimization, an interesting pharmacokinetic analysis has been recently presented [60]. Tabernero and colleagues evaluated the exposure-response relationship of ramucirumab in patients with advanced GC from the REGARD and RAINBOW trials [60]. Interestingly, in both trials, higher levels of ramucirumab exposure were associated with longer PFS and OS, and increased toxicity [60]. These relevant findings justified the decision to increase ramucirumab dose in the ongoing JVCZ trial [61]. This phase II study is evaluating two different doses of ramucirumab (standard dose of 8 mg/kg and experimental dose of 12 mg/kg) in association with paclitaxel in second line treatment of metastatic or locally advanced GC [61]. Another ongoing trial (phase III) aims at exploring the combination of ramucirumab with capecitabine and cisplatin compared to capecitabine and cisplatin only [62]. Ramucirumab is also being evaluated in a phase Ib/2 study in combination with LY2875358, a neutralizing and internalizing bivalent anti-MET antibody [63], in patients with advanced cancers including GC [64].

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VEGF-trap VEGF-trap (also known as aflibercept) is a recombinant fusion protein consisting of VEGF-binding portions from extracellular domains of human VEGF receptors 1 and 2 fused to the Fc portion of human IgG1 [65]. A recent study showed that the combination of trastuzumab plus VEGF-trap, in an HER2-overexpressing GC xenograft model, decreased proliferation, increased apoptosis of tumor cells and decreased tumor vascular density [65]. This combined treatment may represent a valid strategy to delay the emergence of trastuzumab-resistant tumors [65]. Future clinical trials are definitely needed.

Anti-VEGF tyrosine kinase inhibitors Sorafenib Sorafenib is an oral multi-targeted TKI that inhibits VEGFR1, VEGFR-2, VEGFR-3, platelet derived growth factor receptor (PDGFR), B-Raf, Raf-1 and c-Kit [66]. The association between sorafenib and cisplatin plus S-1 showed to be associated with a good tolerability profile [66]. An additional phase I study tested in first-line patients with advanced GC this TKI in combination with cisplatin and capecitabine, leading to a remarkable median OS of 14.7 months and 10 months of PFS [67]. In a subsequent phase II study sorafenib 400 mg orally twice a day for 21 days, was combined with docetaxel 75 mg/m2 intravenously on day 1, and cisplatin 75 mg/m2 intravenously on day 1, repeated every 21 days [68]. OS data (13.6 months) were encouraging and consistent with prior reports [68].

although response rate was significantly increased (41.1 % vs 14.3 %, p = 0.002) [71]. Apatinib Apatinib is a novel, potent TKI that selectively targets VEGFR-2 [72]. A Chinese randomized phase II study evaluated the safety and efficacy of apatinib in patients with metastatic GC refractory to chemotherapy [73]. The final analysis included 144 patients treated with at least 2 lines of treatment; of these, 47 received apatinib 850 mg once a day, 46 apatinib 425 mg twice daily, and 48 placebo [73]. Researchers reported a statistically significant increase in OS and PFS in both treatment groups compared with placebo. The median OS was 4.83 months in the apatinib 850 mg group, 4.27 months in apatinib 425 mg group, and 2.5 months in the placebo group [73]. Notably, three partial responses in the 850 mg group and six in the 425 mg group were observed [73]. The safety data showed a good toxicity profile. The most common G3-4 side effects were limited to hand-foot syndrome and hypertension [73]. The results of the following phase III trial of apatinib vs. placebo have been recently published in abstract form [74]. Two-hundred-seventy heavily pretreated metastatic GC patients were randomly assigned to receive in a 2:1 ratio apatinib (850 mg) or placebo [74]. Median OS (195 days vs. 140 days; HR = 0.71; 95 % CI 0.54-0.94; p < 0.016) and PFS (78 days vs. 53 days, HR = 0.44, 95% CI 0.33-0.61, p < 0.0001) were significantly prolonged in the apatinib arm compared with the placebo arm [74]. As for safety, apatinib confirmed to be tolerable [74]. Findings from both trials are certainly very promising and warrant further evaluation in confirmatory earlier phase clinical trials.

Sunitinib Regorafenib Sunitinib is a further oral multi-targeted TKI which targets RET, VEGFR-1, VEGFR-2, VEGFR-3, PDGFRα, PDGFRβ, Flt 3, c-KIT, and colony-stimulating factor receptor 1 [69]. It has been tested in several phase II trials in pretreated metastatic GC patients, both as a single agent and in combination with chemotherapy [69–71]. Sunitinib was firstly evaluated in 78 patients as second line therapy at 50 mg/day on a 4/2 schedule (4 weeks on treatment, followed by 2 weeks off) [69]. ORR, the primary endpoint, was clearly disappointing (2.6 %), suggesting a very limited activity as single-agent in this setting. An additional phase II study of sunitinib single-agent produced similar negative results [70]. Finally, sunitinib efficacy was explored in combination with docetaxel versus chemotherapy alone in a randomized phase 2 trial involving 105 patients previously treated with fluoropyrimidine and platinum [71]. Again, the addition of TKI to docetaxel did not significantly prolong time to progression (3.9 vs 2.6 months),

Regorafenib (BAY 73–4506) is an oral multi TKI inhibitor targeting VEGFR-2, PDGFR, FGFR-1 and TIE-2 [75]. The phase II INTEGRATE trial investigated the role of regorafenib in refractory advanced EG cancers. Patients received a daily oral dose of 160 mg on days 1–21 each 28-day cycle or a placebo [76]. Median PFS was 11.1 weeks in the experimental arm (95 % CI: 7.7–12.3) and 3.9 with placebo (95 % CI: 3.7– 4.0), p < 0.0001 [76]. Regorafenib is being tested in the phase Ib/II REPEAT trial in combination with paclitaxel in advanced EG adenocarcinoma [77]. Regorafenib tolerability will be tested in a dose escalation scheme with a fixed dose of 80 mg/m2 of paclitaxel on days 1, 8 and 15 of a 28 day cycle [77]. Moreover, a phase II trial is investigating regorafenib as a second line single agent in the treatment of metastatic or advanced adenocarcinoma of the esophagus, GEJ or stomach [78].

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Cediranib and Telatinib These two small molecules were tested in very few patients and demonstrated good tolerability and encouraging results in terms of response rate. Cediranib is a highly potent inhibitor of VEGFR-1 and VEGFR-2 showing also activity against c-Kit and PDGFR [79]. Telatinib is a highly selective, potent and orally available inhibitor of VEGFR, PDGFR and KIT tyrosine kinases [79]. Both are being developed in phase II and III studies in combination with chemotherapy regimens [79]. Table 1 summarizes findings from major phase II-III trials with anti-angiogenic agents in GC. A number of other potential biomarkers are pending clinical validation while some others are still in early development phases.

Targeting MET Aberrant MET signaling has particular importance in GC, with evidence of both overexpression and amplification demonstrated in multiple series [80]. Overexpression of MET occurs in up to 20 % of cases, and is associated with poor prognosis [80]. Amplification of the proto-oncogene MET by fluorescence in situ hybridization (FISH), although overall rare (5–10 %), is detected more frequently in GEJ and intestinal type cancers [81]. Activation of receptor tyrosine kinase MET, whose

Table 1

ligand is represented by hepatocyte growth factor (HGF), leads to proliferation and anti-apoptotic signals [82]. Amplification of MET has been shown to predict response to MET inhibition in many solid tumors [83]. Some trials evaluated the activity of MET inhibitors in GC with conflicting results. Data from a phase II study of foretinib (GSK1363089), a MET TKI, showed no activity in a MET-unselected GC population and minimal activity in patients with concomitant FGFR2 amplification [84]. However, foretinib was well tolerated overall [84]. In a phase I trial enriched for MET-amplified patients, treatment with crizotinib (PF02341066), a multi-targeted TKI, produced significant tumor shrinkage in two out of four patients [85]. Both tumors were located at the GEJ [85]. Another selective, non-ATP competitive, small-molecule inhibitor of c-MET is tivantinib (ARQ 197). Despite a modest efficacy demonstrated in previously treated metastatic GC [86], tivantinib has also been shown to exhibit its antitumor activity in a manner independent of c-MET status by inhibiting microtubule polymerization [87]. MET pathway can additionally be blocked by targeting its natural ligand HGF [88]. In a recently reported double-blind randomized phase II study, the anti-HGF monoclonal antibody rilotumumab (AMG-102) was associated at two different dose levels (7.5 or 15 mg/kg) with ECX chemotherapy and compared to a placebo [89]. PFS, the primary endpoint, was 5.7 months in both rilotumumab groups combined versus 4.2 months in the placebo arm (HR = 0.60, 80 % CI 0.45–

Completed phase II-III clinical trials testing anti-angiogenic drugs in metastatic GC

Anti-angiogenic Trial drug

Line Phase Treatment arms

No. patients

ORR (%)

PFS (months)

OS (months)

Bevacizumab

Shah (2006) [51]

I

II

47

65

8.3

12.3

Bevacizumab

El-Rayes (2010) [52] I

II

38

42

6.6

11.1

Bevacizumab

Shah (2011) [53]

I

II

44

67

12

16.8

Bevacizumab

Ohtsu (2011) [54]

I

III

387 vs 387

46 vs 37

6.7 vs 5.3

12.1 vs 10.1

Ramucirumab

Fuchs (2014) [57]

II

III

238 vs 117

3 vs 3

2.1* vs 1.3

5.2* vs 3.8

Ramucirumab Sorafenib Sunitinib

Wilke (2014) [58] Sun (2010) [68] Bang (2011) [69]

II I II

III II II

Bevacizumab + Irinotecan + Cisplatin Bevacizumab + Docetaxel + Oxaliplatin Bevacizumab + Docetaxel +5-FU+ Leucovorin + Cisplatin Capecitabine + Cisplatin +/− Bevacizumab BSC + Ramucirumab vs BSC + placebo Paclitaxel +/−Ramucirumab Sorafenib + Docetaxel + Cisplatin Sunitinib

330 vs 335 44 78

28* vs 16 39 34.7

4.4* vs 2.9 5.8 2.3

9.6* vs 7.4 13.6 6.8

Sunitinib Sunitinib Apatinib

Moehler (2011) [70] II Yi (2012) [71] II Li (2013) [73] III

II II II

Apatinib

Qin (2014) [74]

III

Sunitinib Docetaxel +/− Sunitinib Placebo vs Apatinib 850 vs Apatinib 425 Apatinib vs Placebo

51 3.9 1.28 3.9 vs 2.6 56 vs 49 41* vs 14 48 vs 47 vs 46 0 vs 6.4 vs 13 1.4 vs 3.67* vs 3.2* 180 vs 90 2.8 vs 0 78 days* vs 53 days

BSC best supportive care *Statistically significant

III

5.81 8 vs 6.6 2.5 vs 4.83* vs 4.27* 195 days* vs 140 days

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0.79; p = 0.016) [89]. In the subgroup biomarker analysis, there was a statistically significant PFS and OS advantage for patients treated with rilotumumab and high c-MET overexpression [89]. On this basis, a phase III trial was performed (RILOMET-1), but stopped early for a higher number of deaths in the experimental arm [90]. Indeed, the addition of rilotumumab to the ECX regimen was detrimental for OS, PFS and ORR compared to placebo [90]. Shah and colleagues, lately presented the first results of a phase II randomized trial of first-line modified FOLFOX6 with or without onartuzumab (previously known as MetMab), a monoclonal antibody to cMET [91]. To be enrolled onto this study, patients (n = 123) were required to have metastatic or recurrent HER2-negative GC and a good performance status [91]. Primary endpoint was PFS evaluated in both intention to treat and MET-positive subgroups (≥ 50 % high IHC staining) [91]. The addition of onartuzumab was ineffective both in the intention to treat analysis and in the subgroup of patients with MET 2+ or 3+ at IHC as it did not improve median OS, PFS and ORR [91]. Nevertheless, two subgroups had an OS advantage with onartuzumab: non Asian patients and patients with no prior gastrectomy regardless of MET status [91]. AMG 337, a novel small molecule TKI of MET, finally seems to be bucking this trend. Specifically, in a phase I trial, Kwak and colleagues evaluated the activity and safety of AMG 337 in 90 patients with different solid tumors [92]. Twenty-one patients (23.3 %) in this study had GEJ, gastric, or esophageal tumors, and 19 (21.1 %) had MET amplification [92]. The daily maximum tolerated dose was 300 mg. Authors reported an impressive 62 % ORR (according to traditional RECIST criteria) in the small subgroup of patients with GEJ cancer harboring MET gene amplification (8 of 13) [92]. The duration of response which included 2 patients on treatment for almost 2 years, was also remarkable [92]. Therapy with AMG 337 was quite well tolerated: most common adverse events included headache, nausea, vomiting and fatigue [92]. These findings are certainly encouraging and confirm that the identification of driver genetic alterations and robust biomarkers is key in clinical research. Phase II studies of AMG 337 monotherapy or in combination with FOLFOX are currently underway [93, 94].

Targeting FGFR2 Another important molecular pathway deregulated in GC involves fibroblast growth factor receptor 2 gene (FGFR2). FGFR2 gene is preferentially amplified and overexpressed in diffuse type tumors playing an important role in gastric carcinoma progression and metastasis [95].

In preclinical studies, small molecule FGFR2 inhibitors such as AZD2171 showed potent inhibition of FGFR2 phosphorylation and cell growth in FGFR2-amplified GC cell lines [96]. Similarly, in chemoresistant GC cell lines, Ki23057, a further novel tyrosine kinase FGFR2 inhibitor, arrested tumor proliferation and demonstrated synergistic antitumor effects especially when used in combination with SN38, PTX, or VP16 significantly [97]. More recently, dovitinib (TKI258, a multitargeting oral TKI with potent inhibitory activity against bFGF receptors 1, 2, 3, VEGF receptors 1, 2, 3, PDGFR and c-KIT) demonstrated robust growth inhibitory activity in FGFR2-amplified GC cell lines [98]. Hopefully, ongoing phase II studies involving dovitinib in association with chemotherapy and AZD2171 will better clarify their role in patients with FGFR-2 amplified GC [99–102].

Targeting PI3K–AKT–mTOR pathway Genetic alterations affecting the PI3K/AKT/mTOR pathway are frequently found in GC [103]. The activation of PI3K pathway starts in response to growth factor stimulation of specific receptors such as EGFR, PDGFR, IGFR, or c-MET [104]. The second step is the phosphorylation of AKT that in turn influences cell cycle progression and angiogenesis and has antiapoptotic effects through the phosphorylation of mTOR [105]. PI3K–AKT–mTOR pathway is frequently activated in GC and has been associated with tumor progression and a worse prognosis [106]. Independently of histology PI3K/AKT and mTOR are reported to be activated in 30 % and 60 % of human GC, respectively [103]. In more recent studies, prevalence of mTOR overexpression was observed in 20 % of gastric tumors [107]. Drugs in clinical development target either a single component of the pathway (e.g. mTOR inhibitors), or act as dual inhibitors (e.g. dual PI3K/mTOR inhibitors). A number of PI3K inhibitors have demonstrated preclinical activity and are being investigated in phase I studies of solid tumors. The PI3K inhibitor LY294002 was used to inhibit growth of implanted tumors of human gastric carcinoma cells in nude mice [108]. It resulted in increasing rates of growth inhibition and was also effective in reducing the tumor expression of a number of angiogenic factors [108]. Similarly, the PI3K/mTOR inhibitor BEZ235 and the PI3K inhibitor BKM120 showed pro-apoptotic effects in human gastric and colon cancer cell lines [109]. A phase Ib trial that combined the PI3K inhibitor BYL719 with the HSP inhibitor (Heat shock protein 90 inhibitor) AUY922 in metastatic HER2 amplified or PI3K mutated GC patients, has just been completed [110]. Hopefully its results will help to clarify the potential benefits of this novel combination.

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Ipatasertib (GDC-0068), a small molecule inhibiting AKT, is under evaluation in a phase II randomized trial. Patients with previously untreated locally advanced or metastatic gastric o GEJ carcinomas are being randomized to receive either chemotherapy with mFOLFOX6 + placebo or the same regimen plus ipatasertib [111]. The PI3K–AKT–mTOR pathway can also be targeted at the mTOR level. A phase II trial was conducted administering everolimus in patients with pretreated metastatic GC. This trial showed a disease control rate of 55 %, although no objective response was noted [112]. The median PFS and OS were 2.7 and 10.1 months, respectively [112]. Based on these results, a phase III randomized multicenter trial compared everolimus plus best supportive care with a placebo plus best supportive care in patients with progressive disease after one or two prior lines of chemotherapy (GRANITE-1) [113]. Median OS was 5.4 months with everolimus and 4.3 months with best supportive care (HR = 0.90, 95 % CI 0.75–1.08, p = 0.124) [112]. The safety profile observed for everolimus was consistent with that observed in other malignancies. The disappointing results of GRANITE-1 underscore the crucial importance of identifying specific and reliable biomarkers in order to better define the specific patient subpopulations that would receive the most benefit from everolimus treatment. For this purpose the results of the ongoing biomarker analyses are eagerly awaited. An interesting randomized phase III trial comparing everolimus plus paclitaxel versus paclitaxel plus placebo in second-line setting is currently recruiting GC patients [114].

Targeting hedgehog inhibitors The sonic hedgehog (SHH) pathway is key for normal cell differentiation and its aberrant activation affects gastric cell proliferation, migration, and invasion [115]. A phase II trial combined vismodegib (an SHH pathway inhibitor) with FOLFOX in patients with advanced gastric and GEJ tumors in a first-line setting [116]. PFS, the primary endpoint, was not met in the intention-to-treat population (11.5 months for FOLFOX plus vismodegib versus 9.3 months for FOLFOX alone, 95 % CI 8.5–14.4, p = 0.34). However, the expression of CD44, a GC stem cell marker, was associated with improved survival in the group who received the SHH inhibitor suggesting that SHH inhibition may only be effective in this particular subgroup [117].

Targeting IGFR Insulin-like growth factors (IGF-I and IGF-II), are potent mitogens for many cell types in the autocrine, paracrine and endocrine pathways. IGF-1R, a ubiquitously expressed tyrosine

kinase receptor, is associated with downstream activation of MAPK/PI3K and is supportive for tumor growth [118, 119]. Few data are available on the expression and biological function of the IGF system in GC. Gryko and colleagues found that the expression of IGF-1R in GC is significantly associated with lymph node metastasis, is correlated with worse prognosis and high histological malignancy grade and is an independent predictor of survival [120]. These data warrant the consideration of IGF-1R as a therapeutical target. Cixutumumab, a fully human IgG1 monoclonal antibody specifically targeting IGF1R, has shown promising antiproliferative activity in vitro and clinically, particularly in soft tissue sarcomas combined with temsirolimus [121]. Cixutumumab was combined with paclitaxel in metastatic esophageal/GEJ cancer in a recently presented randomized phase II study [122]. The primary endpoint (PFS) was not met with median PFS reaching 2.6 months for paclitaxel alone and 2.3 months for paclitaxel + cixutumumab (90 % CI 2–3.6 months, p = 0.72) [122].

Immunotherapy Activating the immune system for achieving therapeutic benefits has long been pursued in cancer medicine. Great interest has been ultimately focused on cancer immunotherapy due to the success of recent proof-of-concept clinical trials [123]. Similarly to other tumors, many immunotherapeutic strategies have been assessed in GEJ cancer in the last two decades. At the present time, the use of checkpoint inhibitors probably represents the most exciting approach which holds the greatest potential for a large diffusion in clinical practice. Cytotoxic T-lymphocyte–associated antigen 4 (CTLA-4), an inhibitory receptor that down-modulates the initial stages of T-cell activation, was the first clinically validated target [124]. Anti–CTLA-4 monoclonal antibodies suppress the CTLA-4-related inhibitory signals resulting in the generation of an antitumor T-cell response [124]. Ipilimumab (Yervoy®, Bristol-Myers Squibb), is an anti– CTLA-4 antibody, that was recently approved for the treatment of patients with stage IV melanoma [125]. Ipilimumab is being evaluated in a global, multicenter, phase II randomized trial as maintenance therapy following first-line chemotherapy in patients with unresectable locally advanced or metastatic gastric or GEJ cancer compared with best supportive care (BSC) [126]. Primary endpoint is immune-related progression free survival, according to the immune related response criteria guidelines [126]. This intriguing study has recently completed its accrual. Due to the innovative design, the results are eagerly awaited. Tremelimumab (CP-675,206, Pfizer) efficacy in advanced gastric and esophageal adenocarcinoma was investigated in a small phase II, single-center, open-label, non-randomized study [127]. Eighteen patients, previously treated with cisplatin-

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based chemotherapy for the metastatic disease, were enrolled. ORR, the primary outcome measure of the study, was only 5 %; however, there was evidence of some clinical benefit as documented by a stable CT scan in a small cohort of patients (4 of 18) [127]. Moreover, one of these patients experienced durable benefit with incremental reduction in tumor burden following each cycle of treatment and a partial response after 25.4 months (8 cycles) of treatment [127]. Most drug-related toxicity was mild [127]. Notably, changes in lymphocyte regulatory phenotype (i.e. forkhead box protein 3 and CTLA-4) and enhanced in vitro proliferative responses to two relevant tumor-associated antigens (i.e. 5T4 and CEA) were detected after treatment [127]. These elements suggest that combining CTLA-4 blockade with antigen-targeted therapy may deserve further investigations.

Table 2

Programmed death 1 (PD-1) protein is another key immune-checkpoint receptor with a chemical structure similar to CTLA-4 but with a distinct biologic function and ligand specificity [128]. PD-L1 is the primary PD-1 ligand that that has been shown to be up-regulated in solid tumors. Blockade of the interaction between PD-1 and PD-L1 potentiates immune responses in vitro and demonstrated preclinical antitumor activity [128]. PD-L1 expression can be found in over 40 % of human gastric carcinoma tissue specimens and is correlated with the infiltration depth of tumor, tumor size lymph node metastasis and poor prognosis [129]. Hence, targeting the interaction between PD-L1 and PD-1 represents an attractive strategy in GC. Safety of BMS-936559 (PD-L1–specific IgG4 monoclonal antibody that inhibits the binding of PD-L1 to both PD-1 and

Selected completed or ongoing clinical trials with novel targeted agents in GC

NCT/Study name/Author

Phase

Targeted Agent

Clinical Setting

Results

MET inhibitors Kwak et al. [92]

1

AMG337

Pretreated GC pts

ORR 62 % in MET amplified pts

NCT02016534 [93] NCT02344810 [94] Shah et al. [84] Shah et al. [91] Iveson et al. [86]

2 1/2 2 2 2

Beyond 1st line; MET+ GC 1st line; MET+ GC 1st or 2nd line; GC 1st line HER2-neg GC 1st line GC

Cunningham et al. [87]

3

AMG 337 AMG 337 + FOLFOX Foretinib FOLFOX +/− Onartuzumab ECX +/− Rilotumumab 7.5 or 15 mg/kg ECX +/− Rilotumumab (R)

1st line GC 15 mg/kg

NA NA NA No difference in PFS and OS PFS 5.7* vs 4.2 months in both Rilotumumab combined arms OS 9.6* (R) vs 11.5 (placebo) months PFS 5.7 months in both arms NA

NCT01611857 [109] FGFR2 inhibitors NCT01457846 [99]

1/2

FOLFOX +/− Tivantinib

1st line GC

2

AZD4547 vs paclitaxel

2nd line GC; FGFR2+

NA

NCT01719549 [98]

2

Dovitinib

2nd or 3rd line, FGFR2 +

NA

NCT01921673 [97] 1/2 Docetaxel +/− Dovitinib NCT01576380 [100] 2 Dovitinib PI3K/AKT/MTOR pathway inhibitors Ohtsu et al. [117] 3 Everolimus vs placebo

2nd line GC 2nd or 3rd line; Scirrhous GC

NA NA

Beyond1st line GC

OS 5.4 vs. 4.3 months PFS: 1.7 vs 1.4 months

NCT01248403 [118] Multi TKI inhibitors Pavlakis et al. [74]

3

Taxol +/− Everolimus

Beyond 1st line; GC

NA

2

Regorafenib vs placebo

2nd or 3rd line; EG carcinoma 2nd line; esophagus, GEJ or stomach

OS 25 vs 19.4 weeks PFS 11.1* vs 3.9 weeks NA

Beyond 1st line GC Beyond first-line;GC PDL1+ Beyond 1st line GC Beyond 1st line; Solid tumors (including GC)

NA ORR 22.2 % NA NA

NCT02241720 [76] 2 Immune checkpoint inhibitors NCT01585987 [131] Muro K. [135] NCT02267343 [136] NCT01928394 [137]

2 1 3 1/2

Regorafenib Ipilimumab Pembrolizumab Nivolumab vs placebo Nivolumab +/−Ipilimumab

Pts patients; NA no data available; FOLFOX (Chemotherapy with Oxaliplatin, Leucovorin Calcium and Fluorouracil); ECX (Chemotherapy with Epirubicin, Cisplatin and Capecitabine) *Statistically significant

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CD80) was evaluated in a phase I study involving 207 patients with metastatic solid tumors - 7 with GC [130]. No responses were observed in the subgroup of GC, but durable tumor regression (ORR of 6 to 17 %) and prolonged control of disease (rates of 12 to 41 % at 24 weeks) were reported in patients with other advanced cancers, including non–small-cell lung cancer, melanoma, and renal-cell cancer [130]. More recently, the phase Ib multicohort KEYNOTE-012 study was presented at 2015 ASCO Gastrointestinal Cancers Symposium [131]. In this study, the PD-1 inhibitor pembrolizumab was evaluated in 39 patients (50 % with prior gastrectomy) with PD-L1–positive metastatic gastric or GEJ cancers (defined as positive PD-L1 staining in the stroma or in at least 1 % of tumor cells) and a good performance status [131]. Patients received a 2-week regimen of pembrolizumab intravenously at 10 mg/kg. At 8.8 months median follow-up, pembrolizumab demonstrated very promising levels of activity [131]. Specifically, among 36 evaluable patients (the majority of whom had received at least two prior therapies for the advanced disease) ORR was 22.2 % according to central review (33.3 % according to investigators). Moreover, over 50 % of patients with measurable disease displayed some degree of tumor shrinkage from baseline. The median duration of response was also remarkably long (24 weeks - range 8+ to 33+ weeks). Median PFS was 1.9 months, and the median OS was not reached at the time of the analysis. Safety of the drug was acceptable [131]. These positive findings support the ongoing development of pembrolizumab for GC. In fact, the phase II KEYNOTE-059 [132] and −061 [133] studies exploring pembrolizumab efficacy in first- and second-line respectively, are currently under way. Additional studies with different immune checkpoints inhibitors are ongoing. Specifically, a phase III study of nivolumab (anti PD-1 monoclonal antibody) versus placebo in patients with gastric carcinoma [134] and a phase I-II study of nivolumab as a single agent or in combination with ipilimumab in different tumor types (triple-negative breast cancer, GC, pancreatic adenocarcinoma, small cell lung cancer and bladder cancer) are currently recruiting participants [135]. Table 2 shows some of the most interesting completed or ongoing clinical trials with novel targeted agents in GC.

ramucirumab, a monoclonal antibody directed against VEGFR2, has been proved to be effective in second-line treatment of unselected metastatic GC patients. A plethora of novel targeted molecules are currently being tested in the clinic. Among these, immune checkpoint inhibitors have shown promise in the treatment of such a difficult to manage disease. Although early results are encouraging, much work remains to be done to improve the outcomes of patients with GC. Largescale genomic studies such as the Cancer Genome Atlas project, have provided physicians with more profound insights of the genomic alterations underlying tumoral process making it possible to classify GC into 4 main molecular subtypes: EBVinfected tumors; MSI tumors; genomically stable tumors; and chromosomally unstable tumors. This new categorization will represent a fundamental tool for identifying new biomarkers and actionable targets. In the near future, prospective trials of molecularly targeted drugs should be necessarily designed for specific patient subgroups accurately selected on a biological basis, in order to ultimately improve outcomes of this deadly disease. Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest.

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5.

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