Review Article
The genomics and therapeutics of HER2-positive gastric cancer— from trastuzumab and beyond Ciara M. Kelly1, Yelena Y. Janjigian1,2 1
Gastrointestinal Oncology Service, Division of Solid Tumor Oncology, Department of Medicine, Memorial Sloan Kettering Cancer Center, New
York, NY 10065, USA; 2Gastrointestinal Oncology Service, Division of Solid Tumor Oncology, Cornell Medical College, New York, NY 10065, USA Contributions: (I) Conception and design: All authors; (II) Administrative support: None; (III) Provision of study materials or patients: None; (IV) Collection and assembly of data: None; (V) Data analysis and interpretation: None; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors. Correspondence to: Yelena Y. Janjigian. 300 E66th Street, Room 1033, New York, NY 10065, USA. Email: [email protected].
Abstract: Gastric cancer is a biologically heterogeneous tumor. The identification of human epidermal growth factor receptor-2 (HER2) biomarker overexpression in gastric cancer represented a significant step towards unraveling the molecular complexity of this disease. Trastuzumab in combination with chemotherapy, in the first-line setting of patients with metastatic, HER2-positive gastric and gastroesophageal, represents the first targeted therapeutic to demonstrate improvement in response rate and survival in gastric cancer. However, not all patients with HER2-positive gastric cancer respond to trastuzumab and the majority of patients who do initially benefit from trastuzumab develop resistance to it. Advances in molecular oncology and cancer genomics have helped to classify gastric cancer into molecularly distinct subtypes. This information informs research efforts investigating the etiology of mechanisms of resistance to HER2directed therapy and guides clinical investigation in methods to overcome this resistance. This article reviews anti-HER2-therapies that are currently used as standard of care in advanced, HER2-positive, breast cancer and are now under investigation as monotherapy and in combination with chemotherapy and/or a second HER2-directed agent in advanced HER2-positive gastric cancer. The future directions of clinical investigation in HER2-positive gastric cancer are also discussed including: novel HER2-directed therapies, the pharmacokinetics and pharmacodynamics of anti-HER2-therapies, the role of functional imaging, the potential of patient derived xenograft preclinical models and the importance of tumor genomic sequencing. Keywords: Esophagogastric junction neoplasms; stomach neoplasms; oncogene protein human epidermal growth factor receptor-2 (oncogene protein HER2); trastuzumab; genomics Submitted Mar 30, 2016. Accepted for publication May 19, 2016. doi: 10.21037/jgo.2016.06.10 View this article at: http://dx.doi.org/10.21037/jgo.2016.06.10
Introduction Globally, gastric cancer is the fifth most common cancer and the third most common cause of cancer related death (1). It is estimated that 43,280 new cases of gastro-esophageal cancer will be diagnosed (2) and 26,420 deaths related to gastro-esophageal cancer will occur in the United States in 2016 (2). The majority of patients diagnosed with gastric cancer present with advanced, incurable disease. Chemotherapy
© Journal of Gastrointestinal Oncology. All rights reserved.
remains the standard of care treatment approach for patients with advanced stage disease however, response rates are relatively low and the prognosis is poor with a median survival of only 8–10 months. This underlines the importance of identifying potential therapeutic targets and developing targeted therapies to improve the outcomes of systemic treatment beyond those currently achieved with conventional chemotherapy. As our understanding of cancer biology, cancer genomics and molecular oncology evolves we now recognize that
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Journal of Gastrointestinal Oncology Vol 7, No 5 October 2016
gastric cancer is not a single disease entity. Gastric cancer represents a conglomerate of histologically and biologically heterogeneous diseases, which are characterized by various genomic alterations that result in activation of molecular pathways. We know more about the biological behavior of gastric cancer and its intrinsic subtypes, particularly the human epidermal growth factor receptor-2 (HER2) amplified gastric cancer subtype. HER2 is the first validated therapeutic target in esophagogastric cancer. The aim of this article is to review HER2-positive gastric cancer, the importance of cancer genomics in classifying this disease entity, the standard therapeutic options available and the future directions of clinical investigation. Pathogenesis One of the most important targets in human malignancy is the epidermal growth factor receptor (EGFR) family. This family includes EGFR/HER1, HER2/neu, HER3 and HER4 (3). Each receptor consists of an extracellular ligand-binding domain, an intracellular domain with kinase activity and a short, lipophilic, transmembrane domain. These receptors are activated by ligand binding however, the specific ligand to HER2 has not been identified yet (4). The HER2-receptor is considered an orphan receptor that is ligand independent. It acts as a co-receptor that modulates signals after ligand binding to other receptors in the EGFR family. Homodimerization independently of a ligand and heterodimerization with other members of the EGFR family produces signals that activates downstream pathways including the Ras/Raf/mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase/protein kinase-B/mammalian target of rapamycin (PI3K/Akt/ mTOR) pathways (5,6). Stimulation of these pathways influences many aspects of tumor cell biology including proliferation, differentiation, migration and apoptosis. The HER2/neu gene located on chromosome 17q21 encodes the HER2-protein. HER2/neu oncogene amplification results in HER2-receptor overexpression. This can enhance and prolong signals that produce advantageous properties for a malignant phenotype transformation by facilitating uncontrolled cell growth and tumorigenesis (7). Incidence The phase III Trastuzumab for Gastric Cancer (ToGA) trial reported the incidence of HER2-positive gastric cancer to be 22% (8). HER2-overexpression in gastric
© Journal of Gastrointestinal Oncology. All rights reserved.
751
cancer is dependent of the location of the primary tumor and ranges between 6–30% (8,9). The reported rates of HER2-positivity are highest in gastro-esophageal junction (GEJ) or stomach cardia tumors compared to tumors arising more distally in the stomach (10). Gastric cancer HER2-overexpression is also influenced by histological subtype. HER2-positivity is predominantly seen in Lauren’s intestinal type, well to moderately differentiated gastric cancers with a low prevalence in diffuse type gastric cancer (32% vs. 6%) (9). HER2 as a prognostic and predictive biomarker Although, HER2-positivity selects the patients most likely to obtain benefit from HER2-targeted therapy some patients with HER2-positive gastric cancer experience primary resistance to HER2-directed therapy. Therefore, HER2-positivity alone is not an adequate predictive biomarker of response to HER2-targeted agents (11). The role of HER2-overexpression as a prognostic biomarker in gastroesophageal cancer is controversial. Retrospective studies have demonstrated HER2-positivity as a poor prognostic marker associated with increased risk of invasion, metastasis and worse survival (12,13). Surgical series have also determined HER2-status to be the second poorest prognostic marker after nodal status (14,15), while other studies have found no association between HER2 and prognosis in both early and advanced stage disease (16,17). Detection of HER2-positivity HER2-positivity is determined by quantification of the HER2 cell surface receptors via immunohistochemistry (IHC) and/or by measuring the number of HER2 gene copy numbers using fluorescent in-situ hybridization (FISH) techniques (Figure 1). In gastric cancer testing for HER2 is recommended in patients with inoperable, locally advanced, recurrent or metastatic disease in whom trastuzumab therapy is being considered (18). Determination of HER2-status via IHC is distinct for gastric cancer. The main difference in scoring HER2 IHC staining between gastric and breast cancer is that an incomplete basolateral or lateral staining alone in gastric cancer is considered positive in addition to complete membrane staining. This results in tumor heterogeneity and the potential for inaccuracy in the detection of HER2positive tumors. In gastric cancer HER2-positivity is determined by 3+
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Kelly and Janjigian. HER2-positive gastric cancer—genomics and therapeutics
752
IHC
200×
HER2 positive (3+)
20×
Equiviocal (2+)
40×
HER2 negative (0-1+)
FISH assay
No further testing
Not amplified
No further testing
Amplified FISH ≥2.0
Figure 1 HER2 testing algorithm. HER2, human epidermal growth factor receptor-2.
scoring on IHC or FISH positivity (HER2: CEP 17 ratio ≥2.0). Due to the higher rate of tumor heterogeneity and incomplete membranous reactivity seen in gastric cancer compared to breast cancer an IHC scoring criteria specific for HER2-overexpression in gastric cancer was devised (19). The IHC staining pattern that determines the highest level of HER2 expression by IHC (IHC 3+) is different depending on whether a surgical specimen or biopsy is tested. Basolateral or lateral membranous reactivity in ≥10% of tumor cells represents an IHC 3+ staining pattern in the setting of a surgical specimen. An IHC 3+ staining pattern on a tumor biopsy is determined by tumor cell clusters with a strong complete, basolateral or lateral membranous reactivity irrespective of percentage of tumor cells stained (8). Tumors with equivocal IHC scores (2+) should be tested further using FISH or other in situ methods. Research efforts are endeavoring to improve the quality and precision with which HER2 status is determined in gastric cancer. A recent study suggested that the proteomicsbased collaborative enzyme enhanced reactive (CEER) immunoassay is a useful technique to investigate HER2 expression in gastric cancer. CEER-based assays showed higher sensitivity and specificity as compared to IHCbased assays (20). Another technique to consider is to use a quantitative variable, as used in breast cancer, that could be objectively measured, such as HER2 gene copy number or the HER2 amplification ratio, compared to the subjective IHC scoring assessment (21).
© Journal of Gastrointestinal Oncology. All rights reserved.
Pathologic concordance High concordance between HER2 status measured on the primary tumor and corresponding sites of metastatic disease has been reported in gastric cancer (17,22). This suggests that the evaluation of HER2 status in the primary tumor alone is sufficient to determine appropriateness for treatment with anti-HER2-therapy in gastro-esophageal cancer. Management of HER2-positive gastroesophageal cancers Inoperable locally advanced/metastatic disease Trastuzumab is a monoclonal anti-body that binds to the extracellular domain of the HER2-receptor blocking its downstream signaling pathway. It promotes an antibodydependent cell-mediated cytotoxicity by activating apoptotic signals in tumor cells (23). The ToGA trial was the first phase III study to investigate the role of trastuzumab in the setting of HER2-positive gastric or GEJ cancer. This open-label, international trial randomized 594 patients to receive a combination of fluoropyrimidine and cisplatin administered every 3 weeks for 6 cycles with or without trastuzumab. This study met its primary end point by demonstrating a significant improvement in overall survival favoring the trastuzumab arm (13.8 vs. 11.1 months; P=0.0046). Overall response rate was also significantly better in the trastuzumab arm (47% vs.
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Journal of Gastrointestinal Oncology Vol 7, No 5 October 2016
35%, P=0.0017). However, this response rate highlights that the considerable proportion of individuals that are primary refractory to HER2-inhibition even in the presence of the drug target. An exploratory analysis identified that the patients with the highest level of HER2 expression (IHC2+ & FISH+ or IHC3+) compared to patients with FISH positivity and low level of HER2 expression via IHC (IHC 0 or 1 & FISH positive) derived the greatest benefit from trastuzumab in combination with chemotherapy (16.0 vs. 11.8 months; HR 0.68; 95% CI, 0.5–0.83). This was not a preplanned exploratory analysis (8). However, as a consequence of this post-hoc exploratory analysis different requirements for the approval of trastuzumab in this indication have emerged in the US and in Europe. The US Food and Drug Administration (FDA) granted trastuzumab approval for use in patients with advanced gastric cancer with positive FISH results or an IHC score 3+ (24). The European Medicines Agency (EMA) limited the approval to patients with gastric cancers with HER2 overexpression as defined by HER2 IHC score 2+, confirmed by a positive FISH result, or by HER2 IHC score of 3+ (25). The ToGA trial also demonstrated safety for the combination of trastuzumab with chemotherapy in gastric cancer. The rates of grade 3 or 4 adverse events were similar between the treatment groups. Notably, the proportion of patients that experienced cardiac dysfunction (defined as a ≥10% drop in LVEF to an absolute value
The genomics and therapeutics of HER2-positive gastric cancer— from trastuzumab and beyond Ciara M. Kelly1, Yelena Y. Janjigian1,2 1
Gastrointestinal Oncology Service, Division of Solid Tumor Oncology, Department of Medicine, Memorial Sloan Kettering Cancer Center, New
York, NY 10065, USA; 2Gastrointestinal Oncology Service, Division of Solid Tumor Oncology, Cornell Medical College, New York, NY 10065, USA Contributions: (I) Conception and design: All authors; (II) Administrative support: None; (III) Provision of study materials or patients: None; (IV) Collection and assembly of data: None; (V) Data analysis and interpretation: None; (VI) Manuscript writing: All authors; (VII) Final approval of manuscript: All authors. Correspondence to: Yelena Y. Janjigian. 300 E66th Street, Room 1033, New York, NY 10065, USA. Email: [email protected].
Abstract: Gastric cancer is a biologically heterogeneous tumor. The identification of human epidermal growth factor receptor-2 (HER2) biomarker overexpression in gastric cancer represented a significant step towards unraveling the molecular complexity of this disease. Trastuzumab in combination with chemotherapy, in the first-line setting of patients with metastatic, HER2-positive gastric and gastroesophageal, represents the first targeted therapeutic to demonstrate improvement in response rate and survival in gastric cancer. However, not all patients with HER2-positive gastric cancer respond to trastuzumab and the majority of patients who do initially benefit from trastuzumab develop resistance to it. Advances in molecular oncology and cancer genomics have helped to classify gastric cancer into molecularly distinct subtypes. This information informs research efforts investigating the etiology of mechanisms of resistance to HER2directed therapy and guides clinical investigation in methods to overcome this resistance. This article reviews anti-HER2-therapies that are currently used as standard of care in advanced, HER2-positive, breast cancer and are now under investigation as monotherapy and in combination with chemotherapy and/or a second HER2-directed agent in advanced HER2-positive gastric cancer. The future directions of clinical investigation in HER2-positive gastric cancer are also discussed including: novel HER2-directed therapies, the pharmacokinetics and pharmacodynamics of anti-HER2-therapies, the role of functional imaging, the potential of patient derived xenograft preclinical models and the importance of tumor genomic sequencing. Keywords: Esophagogastric junction neoplasms; stomach neoplasms; oncogene protein human epidermal growth factor receptor-2 (oncogene protein HER2); trastuzumab; genomics Submitted Mar 30, 2016. Accepted for publication May 19, 2016. doi: 10.21037/jgo.2016.06.10 View this article at: http://dx.doi.org/10.21037/jgo.2016.06.10
Introduction Globally, gastric cancer is the fifth most common cancer and the third most common cause of cancer related death (1). It is estimated that 43,280 new cases of gastro-esophageal cancer will be diagnosed (2) and 26,420 deaths related to gastro-esophageal cancer will occur in the United States in 2016 (2). The majority of patients diagnosed with gastric cancer present with advanced, incurable disease. Chemotherapy
© Journal of Gastrointestinal Oncology. All rights reserved.
remains the standard of care treatment approach for patients with advanced stage disease however, response rates are relatively low and the prognosis is poor with a median survival of only 8–10 months. This underlines the importance of identifying potential therapeutic targets and developing targeted therapies to improve the outcomes of systemic treatment beyond those currently achieved with conventional chemotherapy. As our understanding of cancer biology, cancer genomics and molecular oncology evolves we now recognize that
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Journal of Gastrointestinal Oncology Vol 7, No 5 October 2016
gastric cancer is not a single disease entity. Gastric cancer represents a conglomerate of histologically and biologically heterogeneous diseases, which are characterized by various genomic alterations that result in activation of molecular pathways. We know more about the biological behavior of gastric cancer and its intrinsic subtypes, particularly the human epidermal growth factor receptor-2 (HER2) amplified gastric cancer subtype. HER2 is the first validated therapeutic target in esophagogastric cancer. The aim of this article is to review HER2-positive gastric cancer, the importance of cancer genomics in classifying this disease entity, the standard therapeutic options available and the future directions of clinical investigation. Pathogenesis One of the most important targets in human malignancy is the epidermal growth factor receptor (EGFR) family. This family includes EGFR/HER1, HER2/neu, HER3 and HER4 (3). Each receptor consists of an extracellular ligand-binding domain, an intracellular domain with kinase activity and a short, lipophilic, transmembrane domain. These receptors are activated by ligand binding however, the specific ligand to HER2 has not been identified yet (4). The HER2-receptor is considered an orphan receptor that is ligand independent. It acts as a co-receptor that modulates signals after ligand binding to other receptors in the EGFR family. Homodimerization independently of a ligand and heterodimerization with other members of the EGFR family produces signals that activates downstream pathways including the Ras/Raf/mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3 kinase/protein kinase-B/mammalian target of rapamycin (PI3K/Akt/ mTOR) pathways (5,6). Stimulation of these pathways influences many aspects of tumor cell biology including proliferation, differentiation, migration and apoptosis. The HER2/neu gene located on chromosome 17q21 encodes the HER2-protein. HER2/neu oncogene amplification results in HER2-receptor overexpression. This can enhance and prolong signals that produce advantageous properties for a malignant phenotype transformation by facilitating uncontrolled cell growth and tumorigenesis (7). Incidence The phase III Trastuzumab for Gastric Cancer (ToGA) trial reported the incidence of HER2-positive gastric cancer to be 22% (8). HER2-overexpression in gastric
© Journal of Gastrointestinal Oncology. All rights reserved.
751
cancer is dependent of the location of the primary tumor and ranges between 6–30% (8,9). The reported rates of HER2-positivity are highest in gastro-esophageal junction (GEJ) or stomach cardia tumors compared to tumors arising more distally in the stomach (10). Gastric cancer HER2-overexpression is also influenced by histological subtype. HER2-positivity is predominantly seen in Lauren’s intestinal type, well to moderately differentiated gastric cancers with a low prevalence in diffuse type gastric cancer (32% vs. 6%) (9). HER2 as a prognostic and predictive biomarker Although, HER2-positivity selects the patients most likely to obtain benefit from HER2-targeted therapy some patients with HER2-positive gastric cancer experience primary resistance to HER2-directed therapy. Therefore, HER2-positivity alone is not an adequate predictive biomarker of response to HER2-targeted agents (11). The role of HER2-overexpression as a prognostic biomarker in gastroesophageal cancer is controversial. Retrospective studies have demonstrated HER2-positivity as a poor prognostic marker associated with increased risk of invasion, metastasis and worse survival (12,13). Surgical series have also determined HER2-status to be the second poorest prognostic marker after nodal status (14,15), while other studies have found no association between HER2 and prognosis in both early and advanced stage disease (16,17). Detection of HER2-positivity HER2-positivity is determined by quantification of the HER2 cell surface receptors via immunohistochemistry (IHC) and/or by measuring the number of HER2 gene copy numbers using fluorescent in-situ hybridization (FISH) techniques (Figure 1). In gastric cancer testing for HER2 is recommended in patients with inoperable, locally advanced, recurrent or metastatic disease in whom trastuzumab therapy is being considered (18). Determination of HER2-status via IHC is distinct for gastric cancer. The main difference in scoring HER2 IHC staining between gastric and breast cancer is that an incomplete basolateral or lateral staining alone in gastric cancer is considered positive in addition to complete membrane staining. This results in tumor heterogeneity and the potential for inaccuracy in the detection of HER2positive tumors. In gastric cancer HER2-positivity is determined by 3+
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Kelly and Janjigian. HER2-positive gastric cancer—genomics and therapeutics
752
IHC
200×
HER2 positive (3+)
20×
Equiviocal (2+)
40×
HER2 negative (0-1+)
FISH assay
No further testing
Not amplified
No further testing
Amplified FISH ≥2.0
Figure 1 HER2 testing algorithm. HER2, human epidermal growth factor receptor-2.
scoring on IHC or FISH positivity (HER2: CEP 17 ratio ≥2.0). Due to the higher rate of tumor heterogeneity and incomplete membranous reactivity seen in gastric cancer compared to breast cancer an IHC scoring criteria specific for HER2-overexpression in gastric cancer was devised (19). The IHC staining pattern that determines the highest level of HER2 expression by IHC (IHC 3+) is different depending on whether a surgical specimen or biopsy is tested. Basolateral or lateral membranous reactivity in ≥10% of tumor cells represents an IHC 3+ staining pattern in the setting of a surgical specimen. An IHC 3+ staining pattern on a tumor biopsy is determined by tumor cell clusters with a strong complete, basolateral or lateral membranous reactivity irrespective of percentage of tumor cells stained (8). Tumors with equivocal IHC scores (2+) should be tested further using FISH or other in situ methods. Research efforts are endeavoring to improve the quality and precision with which HER2 status is determined in gastric cancer. A recent study suggested that the proteomicsbased collaborative enzyme enhanced reactive (CEER) immunoassay is a useful technique to investigate HER2 expression in gastric cancer. CEER-based assays showed higher sensitivity and specificity as compared to IHCbased assays (20). Another technique to consider is to use a quantitative variable, as used in breast cancer, that could be objectively measured, such as HER2 gene copy number or the HER2 amplification ratio, compared to the subjective IHC scoring assessment (21).
© Journal of Gastrointestinal Oncology. All rights reserved.
Pathologic concordance High concordance between HER2 status measured on the primary tumor and corresponding sites of metastatic disease has been reported in gastric cancer (17,22). This suggests that the evaluation of HER2 status in the primary tumor alone is sufficient to determine appropriateness for treatment with anti-HER2-therapy in gastro-esophageal cancer. Management of HER2-positive gastroesophageal cancers Inoperable locally advanced/metastatic disease Trastuzumab is a monoclonal anti-body that binds to the extracellular domain of the HER2-receptor blocking its downstream signaling pathway. It promotes an antibodydependent cell-mediated cytotoxicity by activating apoptotic signals in tumor cells (23). The ToGA trial was the first phase III study to investigate the role of trastuzumab in the setting of HER2-positive gastric or GEJ cancer. This open-label, international trial randomized 594 patients to receive a combination of fluoropyrimidine and cisplatin administered every 3 weeks for 6 cycles with or without trastuzumab. This study met its primary end point by demonstrating a significant improvement in overall survival favoring the trastuzumab arm (13.8 vs. 11.1 months; P=0.0046). Overall response rate was also significantly better in the trastuzumab arm (47% vs.
jgo.amegroups.com
J Gastrointest Oncol 2016;7(5):750-762
Journal of Gastrointestinal Oncology Vol 7, No 5 October 2016
35%, P=0.0017). However, this response rate highlights that the considerable proportion of individuals that are primary refractory to HER2-inhibition even in the presence of the drug target. An exploratory analysis identified that the patients with the highest level of HER2 expression (IHC2+ & FISH+ or IHC3+) compared to patients with FISH positivity and low level of HER2 expression via IHC (IHC 0 or 1 & FISH positive) derived the greatest benefit from trastuzumab in combination with chemotherapy (16.0 vs. 11.8 months; HR 0.68; 95% CI, 0.5–0.83). This was not a preplanned exploratory analysis (8). However, as a consequence of this post-hoc exploratory analysis different requirements for the approval of trastuzumab in this indication have emerged in the US and in Europe. The US Food and Drug Administration (FDA) granted trastuzumab approval for use in patients with advanced gastric cancer with positive FISH results or an IHC score 3+ (24). The European Medicines Agency (EMA) limited the approval to patients with gastric cancers with HER2 overexpression as defined by HER2 IHC score 2+, confirmed by a positive FISH result, or by HER2 IHC score of 3+ (25). The ToGA trial also demonstrated safety for the combination of trastuzumab with chemotherapy in gastric cancer. The rates of grade 3 or 4 adverse events were similar between the treatment groups. Notably, the proportion of patients that experienced cardiac dysfunction (defined as a ≥10% drop in LVEF to an absolute value
