REVIEW EDITORIAL For reprint orders, please contact: [email protected]
Circulating tumor cells as biomarkers of head and neck squamous cell carcinoma: an updated view “Further efforts must be put into isolating reliable biomarkers with the objective of improving the survival rate and the patient’s quality of life.” Alberto Mangano*,1,2, Alessandro Mangano1,3, Georgios D Lianos4, Luca Levrini3, Monica Picone5, Luigi Boni1,2 & Gianlorenzo Dionigi1,2 Molecular medicine has become a major factor in modern oncology and medicine, playing a fundamental role in all aspects from diagnosis to the development of new molecular compounds. Since the completion of the Human Genome Project in 2003, we have paved the way to new research roads that have given us the possibility of further understanding the m olecular basis of cancer [1] . Over the last decade, we observed a soar in the scientific discovery of tumor markers and circulating biomarkers that can be exploited as potential diagnostic tools [2] . Notably, the use of such biomarkers as diagnostic tools can play a major role in the diagnostic process allowing early-stage cancer detection, hence changing the relative outcome of the cancer and tackling the overall death rate. Modern medicine must be able to give patients the best possible treatment and it is our duty to shift from ‘old’ nonselective treatments to ‘new tailored treatments’ that must be capable of being highly specific with less adverse effects. In particular, in order to address this issue we have to further explore the role of circulating biomarkers and their effects as diagnostic and prognostic indicators.
In this editorial, we want to capture the essence of the current knowledge about circulating biomarkers in the head and neck squamous cell carcinoma and discuss the future research trends in this field. Head & neck squamous cell carcinoma Head and neck squamous cell carcinoma (HNSCC) is an epithelial cancer affecting different anatomical sites such as the pharynx, larynx and oral cavity [3] . HNSCC currently is the sixth most frequent cancer worldwide and every year 600,000 new cases are diagnosed. In particular, a predominance of oral squamous cell carcinoma is observed and the highest incidence is reported in India due to habits like chewing tobacco and betel quid, which are considered important risk factors [4] . Recently, besides traditional risk factors, such as alcohol consumption and tobacco, human papilloma virus (HPV) related head and neck cancer has emerged as a new distinct group [5,6] . Notably, a different prognosis in HPV-related and non-HPV-related HNSCC has been observed, with a worse survival outcome for the second group [6,7] . In spite of the dramatic improvements
KEYWORDS
• circulating biomarkers • head
and neck squamous cell carcinoma • miRNA • RT-PCR • tumor DNA
“Molecular medicine has become a major factor in modern oncology and medicine, playing a fundamental role in all aspects from diagnosis to the development of new molecular compounds.”
Department of Surgical & Morphological Sciences, Insubria University Varese-Como, Varese, Italy 1st Department of General Surgery Ospedale di Circolo e Fondazione Macchi Varese, Italy 3 Oro Cranio Facial Disease & Medicine Research Center, Insubria University Varese-Como, Varese, Italy 4 Department of General Surgery, Ioannina University Hospital, Centre for Biosystems & Genomic Network Medicine Ioannina University, Ioannina, Greece 5 Private Practice, Palermo, Italy *Author for correspondence: [email protected] ‡ Authors contributed equally 1 2
10.2217/FON.15.115 © 2015 Future Medicine Ltd
Future Oncol. (2015) 11(13), 1851–1853
part of
ISSN 1479-6694
1851
Editorial Mangano, Mangano, Lianos et al. made for early diagnosis, there are still a lot of aspects to be investigated in order to find new biomarkers suitable for an early cancer detection. Nowadays, ‘Omic’ technologies are capable of giving new powerful diagnostic tools and further effort is needed in order to improve, via an early diagnosis, the outcome of such a cancer.
“The discovery in 2000 of miRNAs has opened new frontiers in the field of cancer biomarkers and many ncRNAs have been studied until now.”
1852
Current scenarios, challenges & perspectives The current 5-year survival rate after treatment widely ranges from 15 to 50% [8] , remaining low in spite of the improvements made in terms of early detection. This low survival rate has been attributed to a poor therapeutic response. What is more, recent evidence has highlighted how intratumor heterogeneity may play an important role in treatment outcome and response [9] . In fact, different authors have hypothesized that a small subpopulation of cells known as cancer stem cells (CSCs) are responsible for therapy resistance. These cells have a unique and distinctive feature of self-renewal; moreover, they are capable of further differentiation into progenitor cells [10] . An in-depth understanding of how this cell’s subpopulations interact/intertalk and how we can further develop the isolation and characterization of such CSCs is essential. The development of highly sensitive, specific and low invasive diagnostic techniques could be a turning point in the fight against cancer. Today, besides CSCs, a series of different predictive biomarkers have been identified but none have been clinically validated so far. Notably, current trials are investigating the relationship between ERCC1 expression and response to cisplatin treatment. Furthermore, the levels of the EGF receptor (EGFR) in relation to cetuximab sensitivity have been evaluated [11] . Other trials have focused on investigating both EGFR and ERCC1 as they relate to radiation response [11,12] . To date the evidence is scarce in terms of evaluating the predictive potential of EGFR downstream proteins (i.e., pAkt phospho-Akt, pEGFR; phospho-EGFR or phospho-ERK, pERK) related to radiation or cetuximab response [12,13] . Several studies have attempted to identify biomarkers obtained from post-treatment tumor samples. The utility and reliability of these biomarkers remains questionable and a current matter of debate [12,13] . Additionally, as most studies attempt to identify biomarkers obtained from pretreatment
Future Oncol. (2015) 11(13)
biopsies, the utility of biomarkers obtained from post-treatment tumor samples, including circulating tumor cells, remains unclear. Other investigators focused on developing method of isolation and detection of biomarkers from pretreatment biopsies. To date, one of the most used methods is gradient centrifugation using FycollHypaque where a density selection criterion is used. A major pitfall is a massive substantial loss of cell material during the enrichment phase [14] . On the contrary, immunocytochemical detection using monoclonal antibodies guarantees the possibility of characterizing cells by size, shape, nucleus and plasma. The most advanced detection system is the US FDA approved CellSearch™ System (Veridex, Raritan, NJ, USA). This system is able to characterize circulating tumor cells by mean of identification of epithelial features [15] . Further methods are represented by magnetic cell separation and negative immunomagnetic cell separation. The major problem related to studies conducted using magnetic cell separation is the inability of providing data on the magnetic separation phase. Because of this pitfall, several papers in the scientific literature cannot be used to compare findings. To date, many biomarkers have been investigated; most scientific data are represented by trials conducted using animal models. However, in recent years we have observed an increase in trials evaluating circulating biomarkers in humans. A recent study by Kalfert et al. [16] found a correlation between p16 positivity and oropharyngeal cancer. Furthermore, they have investigated matrix metalloproteinases (MMPs) as possible prognostic and diagnostic markers in patients affected by oropharyngeal, hypopharyngeal and laryngeal cancer. They did not find a correlation between MMP1, -2 or -9 in clinical practice. A recent paper paved the way to the use as circulating prognostic markers for the SIRT gene family (SIRT6 and SIRT7) [17] ; investigators found these genes altered in peripheral blood leukocytes of patients with HNSCC. This paper highlighted the possibility to develop a low invasivity (i.e., a blood examination) diagnostic tool. Further efforts must be put in this direction in order to discover diagnostic and prognostic biomarkers for this condition. In recent years, a potential use of heat shock proteins as diagnostic/prognostic factors and as a therapeutic tool emerged. This family of proteins are a group of chaperons classified into six families: Hsp100, Hsp90, Hsp70, Hsp60,
future science group
Circulating tumor cells as biomarkers of head & neck squamous cell carcinoma Hsp40 and small HSPs [18] . In particular, some researchers have found a potential role of Hsp90 as a diagnostic factor and a potential use as a therapeutic molecular target in patients with HNSCC [19,20] . The discovery in 2000 of miRNAs has opened new frontiers in the field of cancer biomarkers and many ncRNAs have been studied until now. A recent meta-analysis on the prognostic value of different miRNA in patients affected by HNSCC revealed how expression of miR-21, miR-18a, miR-134a, miR-210, miR-181a, miR-19a and miR-155 was associated with poor survival. This systematic review highlighted how these ncRNAs, and in particular miR-21, may be promising markers for prognosis in patients with HNSCC [21] . Site-specific biomarkers have been identified and isolated; an investigation conducted by Hu et al. showed how the expression of miR-21 and miR-375 is related to the disease status of laryngeal squamous cell carcinoma. References 1
2
3
4
5
6
7
8
Dulbecco R. A turning point in cancer research: sequencing the human genome. Science 231, 1055–1056 (1986). Lianos GD, Mangano A, Kouraklis G et al. Dynamic sequencing of circulating tumor DNA: novel noninvasive cancer biomarker. Biomark. Med. 8, 629–632 (2014). Kang H, Kiess A, Chung CH. Emerging biomarkers in head and neck cancer in the era of genomics. Nat. Rev. Clin. Oncol. 12, 11–26 (2015). Facompre N, Nakagawa H, Herlyn M et al. Stem-like cells and therapy resistance in squamous cell carcinomas. Adv. Pharmacol. 65, 235–265 (2012). Mangano A, Mangano A, Lianos GD et al. Breakthrough targeted therapeutic approaches to squamous cell carcinoma of the head and neck. Future Oncol. 11, 9–12 (2015). Mangano A, Mangano A, Lianos GD et al. Head and neck squamous cell carcinoma and human papillomavirus: epidemiology, treatment and future trends. Future Oncol. 11, 889–891 (2015). Wang Y, Wang J, Huang Y. MicroRNAs as new biomarkers for human papilloma virus related head and neck cancers. Cancer Biomark. doi:10.3233/CBM-150464 (2015) (Epub ahead of print).
future science group
9
Editorial
The study concluded that these miRNA can be used as diagnostic markers. Several trials have been conducted highlighting novel insights into cancer diagnosis, and many trials are ongoing trying to establish a correlation between several biomarkers and their diagnostic potential with HNSCC. Further efforts must be put into isolating reliable biomarkers with the objective of improving the survival rate and the patient’s quality of life. Financial & competing interests disclosure The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
Kamangar F, Dores GM, Anderson WF. Patterns of cancer incidence, mortality, and prevalence across five continents: defining priorities to reduce cancer disparities in different geographic regions of the world. J. Clin. Oncol. 24, 2137–2150 (2006). Mangano A, Lianos GD, Mangano A et al. Intratumor heterogeneity: origins, clinical significance and optimal strategies for cancer treatment. Future Oncol. 11, 561–564 (2015).
10 Visvader JE, Lindeman GJ. Cancer stem cells
in solid tumours: accumulating evidence and unresolved questions. Nat. Rev. Cancer. 8, 755–768 (2008). 11 Li G, Sturgis EM, Wang LE et al. Association
of a p73 exon 2 G4C14-to-A4T14 polymorphism with risk of squamous cell carcinoma of the head and neck. Carcinogenesis 25, 1911–1916 (2004). 12 Zhang Z, Shi Q, Wang LE et al. No
Association between hOGG1 Ser-326Cys polymorphism and risk of squamous cell carcinoma of the head and neck. Cancer Epidemiol. Biomarkers Prev. 13, 1081–1083 (2004). 13 Cristofanilli M, Budd GT, Ellis MJ et al.
Circulating tumor cells, disease progression, and survival in metastatic breast cancer. N. Engl. J. Med. 351, 781–791 (2004). 14 Wikner J, Gröbe A, Pantel K et al. Squamous
cell carcinoma of the oral cavity and
circulating tumour cells. World J. Clin. Oncol. 10, 114–124 (2014). 15 Gorges TM, Pantel K. Circulating tumor cells
as therapy related biomarkers in cancer patients. Cancer Immunol. Immunother. 62, 931–939 (2013). 16 Kalfert D, Ludvikova M, Topolcan O et al.
Analysis of preoperative serum levels of MMP1, -2, and -9 in patients with sitespecific head and neck squamous cell cancer. Anticancer Res. 34, 7431–7441 (2014). 17 Lu CT, Hsu CM, Lin PM et al. The potential
of SIRT6 and SIRT7 as circulating markers for head and neck squamous cell carcinoma. Anticancer Res. 34, 7137–7143 (2014). 18 Lianos GD, Alexiou GA, Mangano A et al.
The role of heat shock proteins in cancer. Cancer Lett. 360, 114–1148 (2015). 19 Kaur J, Srivastava A, Ralhan R. Expression of
70-kDa heat shock protein in oral lesions: marker of biological stress or pathogenicity. Oral Oncol. 34, 496–501 (1998). 20 Routray S, Sunkavalli A, Swain N et al.
Emphasizing on heat shock protein 90’s utility in head and neck squamous cell carcinoma treatment. J. Cancer Res. Ther. 9, 583–586 (2013). 21 Jamali Z, Asl Aminabadi N, Attaran R et al.
MicroRNAs as prognostic molecular signatures in human head and neck squamous cell carcinoma: a systematic review and meta-analysis. Oral Oncol. 51, 321–331 (2015).
www.futuremedicine.com
1853
Circulating tumor cells as biomarkers of head and neck squamous cell carcinoma: an updated view “Further efforts must be put into isolating reliable biomarkers with the objective of improving the survival rate and the patient’s quality of life.” Alberto Mangano*,1,2, Alessandro Mangano1,3, Georgios D Lianos4, Luca Levrini3, Monica Picone5, Luigi Boni1,2 & Gianlorenzo Dionigi1,2 Molecular medicine has become a major factor in modern oncology and medicine, playing a fundamental role in all aspects from diagnosis to the development of new molecular compounds. Since the completion of the Human Genome Project in 2003, we have paved the way to new research roads that have given us the possibility of further understanding the m olecular basis of cancer [1] . Over the last decade, we observed a soar in the scientific discovery of tumor markers and circulating biomarkers that can be exploited as potential diagnostic tools [2] . Notably, the use of such biomarkers as diagnostic tools can play a major role in the diagnostic process allowing early-stage cancer detection, hence changing the relative outcome of the cancer and tackling the overall death rate. Modern medicine must be able to give patients the best possible treatment and it is our duty to shift from ‘old’ nonselective treatments to ‘new tailored treatments’ that must be capable of being highly specific with less adverse effects. In particular, in order to address this issue we have to further explore the role of circulating biomarkers and their effects as diagnostic and prognostic indicators.
In this editorial, we want to capture the essence of the current knowledge about circulating biomarkers in the head and neck squamous cell carcinoma and discuss the future research trends in this field. Head & neck squamous cell carcinoma Head and neck squamous cell carcinoma (HNSCC) is an epithelial cancer affecting different anatomical sites such as the pharynx, larynx and oral cavity [3] . HNSCC currently is the sixth most frequent cancer worldwide and every year 600,000 new cases are diagnosed. In particular, a predominance of oral squamous cell carcinoma is observed and the highest incidence is reported in India due to habits like chewing tobacco and betel quid, which are considered important risk factors [4] . Recently, besides traditional risk factors, such as alcohol consumption and tobacco, human papilloma virus (HPV) related head and neck cancer has emerged as a new distinct group [5,6] . Notably, a different prognosis in HPV-related and non-HPV-related HNSCC has been observed, with a worse survival outcome for the second group [6,7] . In spite of the dramatic improvements
KEYWORDS
• circulating biomarkers • head
and neck squamous cell carcinoma • miRNA • RT-PCR • tumor DNA
“Molecular medicine has become a major factor in modern oncology and medicine, playing a fundamental role in all aspects from diagnosis to the development of new molecular compounds.”
Department of Surgical & Morphological Sciences, Insubria University Varese-Como, Varese, Italy 1st Department of General Surgery Ospedale di Circolo e Fondazione Macchi Varese, Italy 3 Oro Cranio Facial Disease & Medicine Research Center, Insubria University Varese-Como, Varese, Italy 4 Department of General Surgery, Ioannina University Hospital, Centre for Biosystems & Genomic Network Medicine Ioannina University, Ioannina, Greece 5 Private Practice, Palermo, Italy *Author for correspondence: [email protected] ‡ Authors contributed equally 1 2
10.2217/FON.15.115 © 2015 Future Medicine Ltd
Future Oncol. (2015) 11(13), 1851–1853
part of
ISSN 1479-6694
1851
Editorial Mangano, Mangano, Lianos et al. made for early diagnosis, there are still a lot of aspects to be investigated in order to find new biomarkers suitable for an early cancer detection. Nowadays, ‘Omic’ technologies are capable of giving new powerful diagnostic tools and further effort is needed in order to improve, via an early diagnosis, the outcome of such a cancer.
“The discovery in 2000 of miRNAs has opened new frontiers in the field of cancer biomarkers and many ncRNAs have been studied until now.”
1852
Current scenarios, challenges & perspectives The current 5-year survival rate after treatment widely ranges from 15 to 50% [8] , remaining low in spite of the improvements made in terms of early detection. This low survival rate has been attributed to a poor therapeutic response. What is more, recent evidence has highlighted how intratumor heterogeneity may play an important role in treatment outcome and response [9] . In fact, different authors have hypothesized that a small subpopulation of cells known as cancer stem cells (CSCs) are responsible for therapy resistance. These cells have a unique and distinctive feature of self-renewal; moreover, they are capable of further differentiation into progenitor cells [10] . An in-depth understanding of how this cell’s subpopulations interact/intertalk and how we can further develop the isolation and characterization of such CSCs is essential. The development of highly sensitive, specific and low invasive diagnostic techniques could be a turning point in the fight against cancer. Today, besides CSCs, a series of different predictive biomarkers have been identified but none have been clinically validated so far. Notably, current trials are investigating the relationship between ERCC1 expression and response to cisplatin treatment. Furthermore, the levels of the EGF receptor (EGFR) in relation to cetuximab sensitivity have been evaluated [11] . Other trials have focused on investigating both EGFR and ERCC1 as they relate to radiation response [11,12] . To date the evidence is scarce in terms of evaluating the predictive potential of EGFR downstream proteins (i.e., pAkt phospho-Akt, pEGFR; phospho-EGFR or phospho-ERK, pERK) related to radiation or cetuximab response [12,13] . Several studies have attempted to identify biomarkers obtained from post-treatment tumor samples. The utility and reliability of these biomarkers remains questionable and a current matter of debate [12,13] . Additionally, as most studies attempt to identify biomarkers obtained from pretreatment
Future Oncol. (2015) 11(13)
biopsies, the utility of biomarkers obtained from post-treatment tumor samples, including circulating tumor cells, remains unclear. Other investigators focused on developing method of isolation and detection of biomarkers from pretreatment biopsies. To date, one of the most used methods is gradient centrifugation using FycollHypaque where a density selection criterion is used. A major pitfall is a massive substantial loss of cell material during the enrichment phase [14] . On the contrary, immunocytochemical detection using monoclonal antibodies guarantees the possibility of characterizing cells by size, shape, nucleus and plasma. The most advanced detection system is the US FDA approved CellSearch™ System (Veridex, Raritan, NJ, USA). This system is able to characterize circulating tumor cells by mean of identification of epithelial features [15] . Further methods are represented by magnetic cell separation and negative immunomagnetic cell separation. The major problem related to studies conducted using magnetic cell separation is the inability of providing data on the magnetic separation phase. Because of this pitfall, several papers in the scientific literature cannot be used to compare findings. To date, many biomarkers have been investigated; most scientific data are represented by trials conducted using animal models. However, in recent years we have observed an increase in trials evaluating circulating biomarkers in humans. A recent study by Kalfert et al. [16] found a correlation between p16 positivity and oropharyngeal cancer. Furthermore, they have investigated matrix metalloproteinases (MMPs) as possible prognostic and diagnostic markers in patients affected by oropharyngeal, hypopharyngeal and laryngeal cancer. They did not find a correlation between MMP1, -2 or -9 in clinical practice. A recent paper paved the way to the use as circulating prognostic markers for the SIRT gene family (SIRT6 and SIRT7) [17] ; investigators found these genes altered in peripheral blood leukocytes of patients with HNSCC. This paper highlighted the possibility to develop a low invasivity (i.e., a blood examination) diagnostic tool. Further efforts must be put in this direction in order to discover diagnostic and prognostic biomarkers for this condition. In recent years, a potential use of heat shock proteins as diagnostic/prognostic factors and as a therapeutic tool emerged. This family of proteins are a group of chaperons classified into six families: Hsp100, Hsp90, Hsp70, Hsp60,
future science group
Circulating tumor cells as biomarkers of head & neck squamous cell carcinoma Hsp40 and small HSPs [18] . In particular, some researchers have found a potential role of Hsp90 as a diagnostic factor and a potential use as a therapeutic molecular target in patients with HNSCC [19,20] . The discovery in 2000 of miRNAs has opened new frontiers in the field of cancer biomarkers and many ncRNAs have been studied until now. A recent meta-analysis on the prognostic value of different miRNA in patients affected by HNSCC revealed how expression of miR-21, miR-18a, miR-134a, miR-210, miR-181a, miR-19a and miR-155 was associated with poor survival. This systematic review highlighted how these ncRNAs, and in particular miR-21, may be promising markers for prognosis in patients with HNSCC [21] . Site-specific biomarkers have been identified and isolated; an investigation conducted by Hu et al. showed how the expression of miR-21 and miR-375 is related to the disease status of laryngeal squamous cell carcinoma. References 1
2
3
4
5
6
7
8
Dulbecco R. A turning point in cancer research: sequencing the human genome. Science 231, 1055–1056 (1986). Lianos GD, Mangano A, Kouraklis G et al. Dynamic sequencing of circulating tumor DNA: novel noninvasive cancer biomarker. Biomark. Med. 8, 629–632 (2014). Kang H, Kiess A, Chung CH. Emerging biomarkers in head and neck cancer in the era of genomics. Nat. Rev. Clin. Oncol. 12, 11–26 (2015). Facompre N, Nakagawa H, Herlyn M et al. Stem-like cells and therapy resistance in squamous cell carcinomas. Adv. Pharmacol. 65, 235–265 (2012). Mangano A, Mangano A, Lianos GD et al. Breakthrough targeted therapeutic approaches to squamous cell carcinoma of the head and neck. Future Oncol. 11, 9–12 (2015). Mangano A, Mangano A, Lianos GD et al. Head and neck squamous cell carcinoma and human papillomavirus: epidemiology, treatment and future trends. Future Oncol. 11, 889–891 (2015). Wang Y, Wang J, Huang Y. MicroRNAs as new biomarkers for human papilloma virus related head and neck cancers. Cancer Biomark. doi:10.3233/CBM-150464 (2015) (Epub ahead of print).
future science group
9
Editorial
The study concluded that these miRNA can be used as diagnostic markers. Several trials have been conducted highlighting novel insights into cancer diagnosis, and many trials are ongoing trying to establish a correlation between several biomarkers and their diagnostic potential with HNSCC. Further efforts must be put into isolating reliable biomarkers with the objective of improving the survival rate and the patient’s quality of life. Financial & competing interests disclosure The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
Kamangar F, Dores GM, Anderson WF. Patterns of cancer incidence, mortality, and prevalence across five continents: defining priorities to reduce cancer disparities in different geographic regions of the world. J. Clin. Oncol. 24, 2137–2150 (2006). Mangano A, Lianos GD, Mangano A et al. Intratumor heterogeneity: origins, clinical significance and optimal strategies for cancer treatment. Future Oncol. 11, 561–564 (2015).
10 Visvader JE, Lindeman GJ. Cancer stem cells
in solid tumours: accumulating evidence and unresolved questions. Nat. Rev. Cancer. 8, 755–768 (2008). 11 Li G, Sturgis EM, Wang LE et al. Association
of a p73 exon 2 G4C14-to-A4T14 polymorphism with risk of squamous cell carcinoma of the head and neck. Carcinogenesis 25, 1911–1916 (2004). 12 Zhang Z, Shi Q, Wang LE et al. No
Association between hOGG1 Ser-326Cys polymorphism and risk of squamous cell carcinoma of the head and neck. Cancer Epidemiol. Biomarkers Prev. 13, 1081–1083 (2004). 13 Cristofanilli M, Budd GT, Ellis MJ et al.
Circulating tumor cells, disease progression, and survival in metastatic breast cancer. N. Engl. J. Med. 351, 781–791 (2004). 14 Wikner J, Gröbe A, Pantel K et al. Squamous
cell carcinoma of the oral cavity and
circulating tumour cells. World J. Clin. Oncol. 10, 114–124 (2014). 15 Gorges TM, Pantel K. Circulating tumor cells
as therapy related biomarkers in cancer patients. Cancer Immunol. Immunother. 62, 931–939 (2013). 16 Kalfert D, Ludvikova M, Topolcan O et al.
Analysis of preoperative serum levels of MMP1, -2, and -9 in patients with sitespecific head and neck squamous cell cancer. Anticancer Res. 34, 7431–7441 (2014). 17 Lu CT, Hsu CM, Lin PM et al. The potential
of SIRT6 and SIRT7 as circulating markers for head and neck squamous cell carcinoma. Anticancer Res. 34, 7137–7143 (2014). 18 Lianos GD, Alexiou GA, Mangano A et al.
The role of heat shock proteins in cancer. Cancer Lett. 360, 114–1148 (2015). 19 Kaur J, Srivastava A, Ralhan R. Expression of
70-kDa heat shock protein in oral lesions: marker of biological stress or pathogenicity. Oral Oncol. 34, 496–501 (1998). 20 Routray S, Sunkavalli A, Swain N et al.
Emphasizing on heat shock protein 90’s utility in head and neck squamous cell carcinoma treatment. J. Cancer Res. Ther. 9, 583–586 (2013). 21 Jamali Z, Asl Aminabadi N, Attaran R et al.
MicroRNAs as prognostic molecular signatures in human head and neck squamous cell carcinoma: a systematic review and meta-analysis. Oral Oncol. 51, 321–331 (2015).
www.futuremedicine.com
1853
