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Genomic Alterations and Targeted Therapy in Gastric and Esophageal Adenocarcinoma

      Abstract

      Purpose

      Gastric and esophageal adenocarcinomas are common and aggressive malignancies. Systemic therapy for these tumors is based primarily on cytotoxic chemotherapy, but outcomes remain poor. Precision medicine, where treatments are tailored to specific molecular abnormalities of tumors, holds great promise for improving outcomes in this disease.

      Methods

      A search was performed in PubMed to identify studies that have characterized the molecular basis of gastric and esophageal adenocarcinoma, as well as clinical trials exploring targeted therapies in this disease.

      Findings

      Recent genomic studies have identified potentially targetable genomic alterations in gastroesophageal adenocarcinoma. Specifically, The Cancer Genome Atlas study defined 4 subgroups of gastric cancer, each harboring distinct genomic features. However, development of targeted therapies for gastroesophageal cancer has been challenging. The only biomarker-driven therapy in clinical practice, trastuzumab for the ~15% of patients with human epidermal growth factor receptor 2−positive disease, is modestly effective, extending median overall survival by 2.7 months. Clinical trials of other targeted therapies, including epidermal growth factor receptor, fibroblast growth factor receptor 2, and MET inhibitors, have had disappointing results so far.

      Implications

      The availability of genomic tools provides an unprecedented opportunity to develop new rational therapeutic strategies. New trial designs of targeted therapies in biomarker-selected patient populations have the potential to improve outcomes in this lethal disease. As these clinical trials are being developed, it is increasingly important to incorporate correlative studies that will allow us to identify biomarkers of response or resistance to targeted therapies.

      Key words

      1. Introduction

      Gastric and esophageal cancers are the fifth most commonly diagnosed cancers, and second leading cause of cancer mortality worldwide, with an estimated 1.4 million new cases and 1.1 million deaths annually.
      • Ferlay J.
      • Soerjomataram I.
      • Dikshit R.
      • et al.
      Cancer incidence and mortality worldwide: sources, methods and major patterns in GLOBOCAN 2012.
      While the overall incidence of gastric cancer is declining, it remains particularly prevalent in developing countries, mostly in Asia and South America. In the Western world, the incidence of esophageal adenocarcinoma and cancers of the gastroesophageal junction has increased 6-fold in recent decades.
      • Pohl H.
      • Sirovich B.
      • Welch H.G.
      Esophageal adenocarcinoma incidence: are we reaching the peak?.
      Gastroesophageal cancers are typically diagnosed at an advanced stage and have a dismal 5-year overall survival of 20% to 25%.
      • Deng N.
      • Goh L.K.
      • Wang H.
      • et al.
      A comprehensive survey of genomic alterations in gastric cancer reveals systematic patterns of molecular exclusivity and co-occurrence among distinct therapeutic targets.
      Systemic therapy for these tumors relies largely on empiric chemotherapy. Several clinical trials testing combination chemotherapy regimens for metastatic gastroesophageal cancer have showed modest results. The most effective multi-agent chemotherapy regimen in a multicenter, randomized, Phase III clinical trial was shown to be EOX (epirubicin, oxaliplatin, and capecitabine), with a median overall survival of 11.2 months.
      • Cunningham D.
      • Starling N.
      • Rao S.
      • et al.
      Capecitabine and Oxaliplatin for Advanced Esophagogastric Cancer.
      Additional first-line options include ECF (epirubicin, cisplatin and 5-fluorouracil), DCF (docetaxel, cisplatin, and 5-fluoroucil), and FOLFOX (5-fluoroucil and oxaliplatin).
      • Cunningham D.
      • Starling N.
      • Rao S.
      • et al.
      Capecitabine and Oxaliplatin for Advanced Esophagogastric Cancer.
      • Shah M.A.
      • Janjigian Y.Y.
      • Stoller R.
      • et al.
      Randomized Multicenter Phase II Study of Modified Docetaxel, Cisplatin, and Fluorouracil (DCF) Versus DCF Plus Growth Factor Support in Patients With Metastatic Gastric Adenocarcinoma: A Study of the US Gastric Cancer Consortium.
      • Al-Batran S.E.
      • Hartmann J.T.
      • Probst S.
      • et al.
      Phase III Trial in Metastatic Gastroesophageal Adenocarcinoma with Fluorouracil, Leucovorin Plus Either Oxaliplatin or Cisplatin: A Study of the Arbeitsgemeinschaft Internistische Onkologie.
      However, overall survival with empiric chemotherapy remains <12 months and new, effective therapeutic strategies are urgently needed.
      To develop new therapies, we need to advance our understanding of the biology of these tumors. During the past decade, several studies have shed light on the molecular basis of gastric and esophageal cancer. Most recently, The Cancer Genome Atlas (TCGA) project led to a comprehensive molecular classification of gastric cancer and the identification of genomic alterations that represent potential therapeutic targets.
      The Cancer Genome Atlas Research Network. Comprehensive molecular characterization of gastric adenocarcinoma.
      Similar studies in esophageal cancer have described the genomic landscape of this disease and revealed candidate driver oncogenic events that can be targeted therapeutically.

      2. Methods

      PubMed was searched using the terms genomics and gastric cancer, genomics and esophageal adenocarcinoma, targeted therapy and gastric cancer, targeted therapy and esophageal adenocarcinoma and targeted therapy and gastroesophageal adenocarcinoma. Only English-language clinical trials in humans published between 2005 and December 30, 2015 were included. ClinicalTrials.gov, the American Society of Clinical Oncology annual meeting, and American Society of Clinical Oncology Gastrointestinal Cancers Symposium abstracts from 2005 to 2015 were queried for trials.

      3. Results

      3.1 Molecular Characteristics of Gastric and Esophageal Adenocarcinoma

      3.1.1 Molecular Profiling of Gastric Cancer

      The most comprehensive molecular characterization of gastric cancer was performed by the TCGA Research Network in 2014.
      The Cancer Genome Atlas Research Network. Comprehensive molecular characterization of gastric adenocarcinoma.
      In this study, the TCGA investigators evaluated the mutations, copy-number alterations, gene expression, and DNA methylation of 295 primary gastric adenocarcinomas. This unsupervised analysis led to the identification of 4 subtypes of gastric cancer with distinct features.
      Of these tumors, approximately 9% were Epstein-Barr virus−associated, 22% were hypermutated or microsatellite unstable, 20% were genomically stable, and 50% were tumors with chromosomal instability (CIN) (Figure 1). Epstein-Barr virus−associated tumors showed DNA hypermethylation and a strong predilection for PIK3CA mutations, with 80% of tumors harboring nonsilent PIK3CA mutations. Phosphoinositide 3 kinase inhibitors should therefore be evaluated in Epstein-Barr virus−positive gastric cancer. Another important feature of this group was JAK2, PDL1, and PDL2 amplification and overexpression, suggesting that PD-1 and PDL-1 antibodies and JAK2 inhibitors may be effective in this subtype of gastric cancer.
      Figure 1.
      Figure 1Comprehensive molecular characterization of gastric adenocarcinoma by The Cancer Genome Atlas Network identified 4 subgroups with distinct genomic features: tumors with chromosomal instability, 50%; tumors with microsatellite instability (MSI), 22%; genomically stable tumors, 19%; and Epstein-Barr virus (EBV)−associated tumors, 9%.
      The microsatellite unstable tumors were hypermutated with recurrent PIK3CA (42%) and ERBB3 (26%) mutations, as well as MLH1 hypermethylation. Given the immunogenicity of these tumors due to the high mutational load and the promising results of PD-1 blockade in microsatellite-unstable tumors,
      • Le D.T.
      • Uram J.N.
      • Wang H.
      • et al.
      PD-1 Blockade in Tumors with Mismatch-Repair Deficiency.
      checkpoint inhibition warrants evaluation in this subclass of gastric cancer.
      The third subgroup of gastric cancer was the tumors that lacked aneuploidy and high mutation rates and were therefore classified as genomically stable tumors. These tumors were enriched for the diffuse histologic subtype and harbored CDH1 somatic mutations (37%). In addition, approximately 30% of them had alterations of the RHO signaling pathway, somatic mutations of RHOA, and fusion genes involving the activating proteins of the RHO GTPase. These alterations implicate cell motility in the pathogenesis and progression of these tumors. However, further research is needed to functionally investigate these alterations and develop rational therapeutic strategies for this subclass of gastric adenocarcinoma.
      The largest subgroup, comprising half of the tumors tested within TCGA, were the aneuploid tumors or tumors with CIN. In addition to recurrent TP53 mutations (71%), these tumors harbored focal amplifications of receptor tyrosine kinases (HER2, EGFR, FGFR2, MET), cell cycle regulators (CCNE1, CCND1, CDK4, CDK6), KRAS and VEGFA). A separate series of 116 advanced or metastatic gastric cancer cases confirmed alterations in these genes.
      • Ali S.M.
      • Sanford E.M.
      • Klempner S.J.
      • et al.
      Prospective comprehensive genomic profiling of advanced gastric carcinoma cases reveals frequent clinically relevant genomic alterations and new routes for targeted therapies.
      As targeted therapies against most of these alterations are either in clinical use or in development, biomarker-driven trials utilizing these drugs in CIN gastric cancer should be pursued.

      3.1.2 Molecular Profiling of Esophageal Adenocarcinoma

      Genomic studies in esophageal adenocarcinoma have also been reported in the past few years. In one of the largest series, exome and whole-genome sequencing of 149 esophageal adenocarcinomas revealed recurrent amplifications of EGFR (16%), HER2 (19%), MET (6%), KRAS (21%), CCND1 (10%), CCNE1 (12%), and CDK6 (17%).
      • Dulak A.M.
      • Stojanov P.
      • Peng S.
      • et al.
      Exome and whole-genome sequencing of esophageal adenocarcinoma identifies recurrent driver events and mutational complexity.
      Similar to the CIN subclass of gastric cancer, TP53 mutations were identified in 70% of cases, whereas other tumor suppressor genes were mutated at lower rates (CDKN2A or p16INK4A 12%; SMAD4 8%; SMARCA4 8%; and ARID1A 8%). Using a targeted next-generation sequencing panel of 315 genes, Wang et al profiled 231 esophageal adenocarcinomas and confirmed the presence of recurrent amplifications of receptor tyrosine kinases and cell cycle regulators.
      • Wang K.
      • Johnson A.
      • Ali S.M.
      • et al.
      Comprehensive Genomic Profiling of Advanced Esophageal Squamous Cell Carcinomas and Esophageal Adenocarcinomas Reveals Similarities and Differences.
      As in gastric cancer, these genomic alterations are clinically relevant and further evaluation of therapies against these targets is warranted.

      3.2 Targeted Therapies in Gastroesophageal Cancer

      In many other cancers, use of genomic biomarkers to guide targeted therapy has had marked success. However, in gastroesophageal cancer, the only biomarker-driven therapy in clinical practice is trastuzumab, a humanized monoclonal antibody targeting human epidermal growth factor receptor 2 (HER2). Various targeted therapies have been explored in the treatment of advanced gastroesophageal cancer, but have shown limited efficacy (Table I).
      Table ICompleted randomized clinical trials of targeted therapies in gastric and esophageal adenocarcinoma.
      TherapyStudy
      All studies are Phase III trials except for the SHINE trial, which was a randomized Phase II trial.
      Line of TherapyTreatmentORR (%)Median OS (mo)P
      HER2
       TrastuzumabToGAFirstCX + trastuzumab vs CX47 vs 3513.8 vs 11.10.0046
       LapatinibTRIO-013/LOGiCFirstCapeOx + lapatinib vs CapeOx53 vs 3912.2 vs 10.50.3492
       LapatinibTyTANSecondPaclitaxel + lapatinib vs paclitaxel27 vs 911.0 vs 8.90.1044
      EGFR
       CetuximabEXPANDFirstCX + cetuximab vs CX30 vs 299.4 vs 10.70.95
       PanitumumabREAL-3FirstEOX + panitumumab vs EOX46 vs 428.8 vs 11.30.013
      FGFR2
       AZD4547SHINESecondAZD4547 vs paclitaxelMedian PFS (mo)1.8 vs 3.5
      HGF and MET
       RilotumumabRILOMET-1FirstECX + rilotumumab vs ECX30 vs 399.6 vs 11.50.0016
       OnartuzumabMETGastricFirstFOLFOX + onartuzumab vs FOLFOX11.3 vs 11.00.244
      VEGF-A and VEGFR-2
       BevacizumabAVAGASTFirstCX + bevacizumab vs CX46 vs 3712.1 vs 10.10.1002
       RamucirumabREGARDSecondRamucirumab vs placebo3.4 vs 2.65.2 vs 3.80.047
       RamucirumabRAINBOWSecondPaclitaxel + ramucirumab vs Paclitaxel28 vs 169.6 vs 7.40.017
      CapeOx = capecitabine + oxaliplatin; CX = cisplatin + capecitabine; EGFR = epidermal growth factor receptor; EOX = epirubicin + oxaliplatin + capexitabine; FGFR = fibroblast growth factor receptor; FOLFOX = 5-fluorouracil + leucovorin + oxaliplatin; HGF = hepatocyte growth factor; ORR = overall response rate; OS = overall survival; PFS = progression-free survival VEGF = vascular endothelial growth factor; VEGFR = vascular endothelial growth factor receptor.
      low asterisk All studies are Phase III trials except for the SHINE trial, which was a randomized Phase II trial.

      3.2.1 HER2

      HER2 is a member of the human epidermal growth factor receptor family and is found to be amplified in 15% to 20% of gastric and esophageal adenocarcinomas. In contrast to breast cancer,
      • Slamon D.J.
      • Clark G.M.
      • Wong S.G.
      • Levin W.J.
      • Ullrich A.
      • McGuire W.L.
      Human breast cancer: correlation of relapse and survival with amplification of the HER-2/neu oncogene.
      • Seshadri R.
      • Firgaira F.A.
      • Horsfall D.J.
      • McCaul K.
      • Setlur V.
      • Kitchen P.
      Clinical significance of HER-2/neu oncogene amplification in primary breast cancer. The South Australian Breast Cancer Study Group.
      the prognostic role of HER2 in gastroesophageal cancer is less clear, with some studies associating HER2 overexpression with poor overall survival (OS) and others reporting no significant effect on OS.
      • Janjigian Y.Y.
      • Werner D.
      • Pauligk C.
      • et al.
      Prognosis of metastatic gastric and gastroesophageal junction cancer by HER2 status: a European and USA International collaborative analysis.
      • Tanner M.
      • Hollmén M.
      • Junttila T.T.
      • et al.
      Amplification of HER-2 in gastric carcinoma: association with Topoisomerase IIalpha gene amplification, intestinal type, poor prognosis and sensitivity to trastuzumab.
      Trastuzumab was initially developed and approved for HER2-overexpressing metastatic breast cancer, where, in combination with chemotherapy, it significantly prolonged OS compared with chemotherapy alone (OS 25.1 vs 20.3 months, P = 0.046).
      • Slamon D.J.
      • Leyland-Jones B.
      • Shak S.
      • et al.
      Use of chemotherapy plus a monoclonal antibody against HER2 for metastatic breast cancer that overexpresses HER2.
      Given the positive results in breast cancer and the high prevalence of HER2 amplification and overexpression in gastroesophageal cancer, investigation of trastuzumab was pursued. The ToGA (Trastuzumab for Gastric Cancer) trial was a multicenter, Phase III trial that randomly assigned patients with advanced or metastatic HER2-positive gastroesophageal cancer to receive 5-fluorouracil or capecitabine and cisplatin, with or without trastuzumab.
      • Bang Y.-J.
      • Van Cutsem E.
      • Feyereislova A.
      • et al.
      Trastuzumab in combination with chemotherapy versus chemotherapy alone for treatment of HER2-positive advanced gastric or gastro-oesophageal junction cancer (ToGA): a phase 3, open-label, randomised controlled trial.
      Patients were eligible if their tumor samples were scored as 3+ by immunohistochemistry (IHC) or were fluorescence in situ hybridization (FISH)−positive (HER2 to CEP17 ratio ≥2). Of 3,665 patients screened, 810 (22%) patients were HER2-positive and 594 were randomly assigned to treatment. The patients assigned to receive trastuzumab had a higher overall response rate (47% vs 35%; p = 0.0017) and longer median progression-free (PFS) (6.7 vs 5.5 months; P = 0.0002) and median OS (13.8 vs 11.1 months; P = 0.0046). The benefit of trastuzumab was greater in patients whose tumors were 3+ by IHC or 2+ by IHC and FISH-positive (median OS 16.0 vs 11.8 months; hazard ratio [HR] = 0.65; 95% CI, 0.51−0.83). Based on the results of the ToGA trial, trastuzumab with fluopyrimidine and cisplatin was established as the standard first-line therapy for patients with HER2-positive gastroesophageal cancer.
      Following the paradigm of HER2-positive breast cancer, small molecule inhibitors of HER2 were subsequently tested. Based on preclinical data and a Phase II trial of single-agent lapatinib, which showed a 9% response rate in patients with gastroesophageal adenocarcinoma,
      • Iqbal S.
      • Goldman B.
      • Fenoglio-Preiser C.M.
      • et al.
      Southwest Oncology Group study S0413: a phase II trial of lapatinib (GW572016) as first-line therapy in patients with advanced or metastatic gastric cancer.
      2 Phase III trials of lapatinib in HER2-positive gastroesophageal cancer were launched. The TRIO-013 and LOGiC (Translational Research in Oncology and Lapatinib Optimization Study in the HER2-Positive Gastric Cancer) trial was a multicenter, double-blind, Phase III trial that randomly assigned patients with previously untreated HER2-positive advanced or metastatic gastroesophageal cancer to receive capecitabine and oxaliplatin plus lapatinib or placebo.
      • Hecht J.R.
      • Bang Y.-J.
      • Qin S.K.
      • et al.
      Lapatinib in Combination With Capecitabine Plus Oxaliplatin in Human Epidermal Growth Factor Receptor 2-Positive Advanced or Metastatic Gastric, Esophageal, or Gastroesophageal Adenocarcinoma: TRIO-013/LOGiC- A Randomized Phase III Trial.
      Although patients in the lapatinib arm had a significantly higher response rate compared with patients on placebo (53% vs 39%; P = 0.0031), the study failed to reach its primary end point, with no significant improvement in OS (median OS 12.2 vs 10.5 months; HR = 0.91; 95% CI, 0.73−1.12; P = 0.3492). Preplanned exploratory subgroup analyses revealed an OS benefit of lapatinib in Asian patients (16.5 vs 10.9 months; HR = 0.68; 95% CI, 0.48−0.96; P = 0.0261) and in younger patients (12.9 vs 9.0 months; HR = 0.69; 95% CI, 0.51−0.94; P = 0.0141). No correlation was observed between IHC status and survival. Further biomarker analysis has not been reported yet. The TyTAN (Lapatinib [Tykerb] with Paclitaxel [Taxol] in Asian ErbB2+ [HER2+] Gastric Cancer Study) study was a Phase III trial of paclitaxel with or without lapatinib in the second-line treatment of advanced or metastatic HER2-positive gastric cancer in Asian patients.
      • Satoh T.
      • Xu R.-H.
      • Chung H.-C.
      • et al.
      Lapatinib plus paclitaxel versus paclitaxel alone in the second-line treatment of HER2-amplified advanced gastric cancer in Asian populations: TyTAN--a randomized, phase III study.
      Median OS did not differ between the 2 arms (11.0 vs 8.9 months; HR = 0.84; 95% CI, 0.64−1.11; P = 0.1044). Subgroup analysis found a significant OS benefit for patients with 3+ IHC (14 vs 7.6 months; HR = 0.59; 95% CI, 0.59−0.93; P = 0.0176). Of note, for both LOGiC and TyTAN, the biomarker for enrollment on the trials was the presence of HER2 amplification (FISH-positive, HER2 to CEP17 ≥2), regardless of HER2 expression by IHC. In a recent series of patients with metastatic gastric cancer treated with trastuzumab plus chemotherapy, a higher HER2 to CEP17 ratio of 4.7 was identified as the optimal cutoff to predict response to HER2 directed therapy.
      • Gomez-Martin C.
      • Plaza J.C.
      • Pazo-Cid R.
      • et al.
      Level of HER2 Gene Amplification Predicts Response and Overall Survival in HER2-Positive Advanced Gastric Cancer Treated With Trastuzumab.
      Similar analyses from the LOGiC and TyTAN trials will be useful to establish predictive biomarkers for response to lapatinib.
      Newer HER2-targeted therapies are currently being evaluated, in both the first- and second-line setting. Pertuzumab, a monoclonal antibody that blocks the heterodimerization of HER2 with other HER family members, is being investigated as first-line therapy in combination with trastuzumab and chemotherapy in the Phase III JACOB (A Study of Perjeta [Pertuzumab] in Combination with Herceptin [Trastuzumab] and Chemotherapy in Patients with HER2-Positive Metastatic Gastroesophageal Junction or Gastric Cancer) trial (ClinicalTrials.gov ID: NCT01774786). Trastuzumab emtansine is an antibody−drug conjugate that combines trastuzumab with the cytotoxic agent DM1 and has been approved for the treatment of trastuzumab-refractory, HER2-positive metastatic breast cancer. The Phase II/III GATSBY (A Study of Trastuzumab Emtansine Versus Taxane in Patients With Advanced Gastric Cancer) trial is evaluating the efficacy of trastuzumab emtansine compared with taxane as second-line therapy for patients with advanced or metastatic HER2-positive gastroesophageal cancer (ClinicalTrials.gov ID: NCT01641939). Afatinib is a second-generation irreversible tyrosine kinase inhibitor of EGFR and HER2 and may be more effective than lapatinib. A Phase II study of afatinib in combination with trastuzumab in patients with trastuzumab-refractory HER2-positive advanced gastric cancer is under way (ClinicalTrials.gov ID: NCT01522768).

      3.2.2 Epidermal Growth Factor Receptor

      The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase of the HER family and is amplified in 10% to 15% of esophageal adenocarcinomas and gastric cancers, primarily the CIN subtype.
      The Cancer Genome Atlas Research Network. Comprehensive molecular characterization of gastric adenocarcinoma.
      • Dulak A.M.
      • Stojanov P.
      • Peng S.
      • et al.
      Exome and whole-genome sequencing of esophageal adenocarcinoma identifies recurrent driver events and mutational complexity.
      However, a higher proportion (27%−55%) of these tumors overexpress EGFR.
      • Kim M.A.
      • Lee H.S.
      • Lee H.E.
      • Jeon Y.K.
      • Yang H.K.
      • Kim W.H.
      EGFR in gastric carcinomas: prognostic significance of protein overexpression and high gene copy number.
      • Langer R.
      • Rahden Von B.H.A.
      • Nahrig J.
      • et al.
      Prognostic significance of expression patterns of c-erbB-2, p53, p16INK4A, p27KIP1, cyclin D1 and epidermal growth factor receptor in oesophageal adenocarcinoma: a tissue microarray study.
      To date, multiple trials of EGFR-directed agents in combination with chemotherapy have failed to improve outcomes. Large, Phase III studies have primarily focused on monoclonal antibodies against EGFR (cetuximab and panitumumab), while smaller, Phase II trials have studied the activity of EGFR tyrosine kinase inhibitors. The EXPAND (Capecitabine and cisplatin with or without cetuximab for patients with previously untreated advanced gastric cancer) study was a multicenter, Phase III trial of cisplatin and capecitabine with or without cetuximab in patients with previously untreated advanced or metastatic gastroesophageal adenocarcinoma.
      • Lordick F.
      • Kang Y.-K.
      • Chung H.-C.
      • et al.
      Capecitabine and cisplatin with or without cetuximab for patients with previously untreated advanced gastric cancer (EXPAND): a randomised, open-label phase 3 trial.
      This study showed no difference in PFS or OS between the 2 arms (median PFS 4.4 vs 5.6 months; HR = 1.09; 95% CI, 0.92−1.29; P = 0.32; median OS 9.4 vs 10.7 months; HR = 1.0; 95% CI, 0.87−1.17; P = 0.95). Exploratory analysis showed a tendency toward improved survival for patients with EGFR overexpressing tumors who received cetuximab plus chemotherapy.
      • Lordick F.
      • Kang Y.-K.
      • Salman P.
      • et al.
      Clinical outcome according to tumor HER2 status and EGFR expression in advanced gastric cancer patients from the EXPAND study.
      Equally disappointing results were reported from the REAL-3 (Epirubicin, oxaliplatin, and capecitabine with or without panitumumab for patients with previously untreated advanced esophagogastric cancer) trial, which randomly assigned patients with previously untreated advanced gastroesophagal cancer to EOX with or without panitumumab, a fully human monoclonal antibody against EGFR.
      • Waddell T.
      • Chau I.
      • Cunningham D.
      • et al.
      Epirubicin, oxaliplatin, and capecitabine with or without panitumumab for patients with previously untreated advanced oesophagogastric cancer (REAL3): a randomised, open-label phase 3 trial.
      The addition of panitumumab to EOX not only failed to improve outcomes, but also had a detrimental effect on OS (8.8 vs 11.3 months; HR = 1.37; 95% CI, 1.07−1.76; P = 0.013). Trials investigating EGFR tyrosine kinase inhibitors have also shown modest results, with objective response rates ranging from 0 to 11%.
      • Ferry D.R.
      • Anderson M.
      • Beddard K.
      • et al.
      A phase II study of gefitinib monotherapy in advanced esophageal adenocarcinoma: evidence of gene expression, cellular, and clinical response.
      • Janmaat M.L.
      • Gallegos-Ruiz M.I.
      • Rodriguez J.A.
      • et al.
      Predictive factors for outcome in a phase II study of gefitinib in second-line treatment of advanced esophageal cancer patients.
      • Dragovich T.
      • McCoy S.
      • Fenoglio-Preiser C.M.
      • et al.
      Phase II trial of erlotinib in gastroesophageal junction and gastric adenocarcinomas: SWOG 0127.
      Notably, all EGFR-directed trials were performed in unselected patient populations, which might explain the disappointing results. However, a recent preclinical study in patient-derived xenograft models of gastric cancer showed that tumors with EGFR amplification and overexpression had a marked response to cetuximab.
      • Zhang L.
      • Yang J.
      • Cai J.
      • et al.
      A subset of gastric cancers with EGFR amplification and overexpression respond to cetuximab therapy.
      Further evaluation of EGFR inhibitors is therefore warranted in a carefully selected patient population, primarily the ones with EGFR-amplified gastroesophageal cancer.

      3.2.3 Fibroblast Growth Factor Receptor 2

      Fibroblast growth factor receptor 2 (FGFR2) is a receptor tyrosine kinase that plays key roles in cell proliferation, differentiation, and migration. FGFR2 amplification occurs in 4% to 10% of gastric and esophageal adenocarcinomas and is associated with a poor prognosis.
      • Su X.
      • Zhan P.
      • Gavine P.R.
      • et al.
      FGFR2 amplification has prognostic significance in gastric cancer: results from a large international multicentre study.
      A biomarker-driven clinical trial investigating the efficacy of FGFR inhibition was recently reported.
      • Bang Y.-J.
      • Van Cutsem E.
      • Mansoor W.
      • et al.
      A randomized, open-label phase II study of AZD4547 (AZD) versus Paclitaxel (P) in previously treated patients with advanced gastric cancer (AGC) with Fibroblast Growth Factor Receptor 2 (FGFR2) polysomy or gene amplification (amp): SHINE study.
      The SHINE (Efficacy and Safety of AZD4547 Versus Paclitaxel in Advanced Gastric or Gastroesophageal Junction Cancer Patients) study was a randomized Phase II trial that compared the FGFR inhibitor AZD4547 with paclitaxel in the second-line setting in FGFR2-amplified advanced gastric cancer. Of 960 patients screened, 71 were randomized to AZD4547 or paclitaxel. Median PFS was 1.8 months for the AZD4547 arm vs 3.5 months for the paclitaxel arm. Interestingly, exploratory biomarker analysis revealed marked intra-tumor heterogeneity of FGFR2 amplification, with 4 of 7 tumors tested showing amplification in <20% of the tumor section. Furthermore, only 21% of FGFR2-amplified tumors had high FGFR2 expression. Although the correlation of intra-tumor heterogeneity and FGFR2 expression with response to AZD4547 were not reported, both these factors might explain the lack of efficacy of FGFR inhibition. Additional clinical trials exploring the activity of the FGFR2 inhibitor dovitinib in the second and third-line setting are ongoing (ClinicalTrials.gov ID: NCT01719549). Correlative studies to identify biomarkers that could predict response or resistance to FGFR inhibition will be essential.

      3.2.4 MET

      Dysregulation of the MET and hepatocyte growth factor pathway promotes tumor growth and metastasis in gastroesophageal cancer. Although MET amplification is found in approximately 6% of gastroesophageal cancer,
      The Cancer Genome Atlas Research Network. Comprehensive molecular characterization of gastric adenocarcinoma.
      ,
      • Dulak A.M.
      • Stojanov P.
      • Peng S.
      • et al.
      Exome and whole-genome sequencing of esophageal adenocarcinoma identifies recurrent driver events and mutational complexity.
      ,
      • Wang K.
      • Johnson A.
      • Ali S.M.
      • et al.
      Comprehensive Genomic Profiling of Advanced Esophageal Squamous Cell Carcinomas and Esophageal Adenocarcinomas Reveals Similarities and Differences.
      MET expression has been reported in 46% to 74% of cases.
      • Nakajima M.
      • Sawada H.
      • Yamada Y.
      • et al.
      The prognostic significance of amplification and overexpression of c-met and c-erb B-2 in human gastric carcinomas.
      • Drebber U.
      • Baldus S.E.
      • Nolden B.
      • et al.
      The overexpression of c-met as a prognostic indicator for gastric carcinoma compared to p53 and p21 nuclear accumulation.
      • Janjigian Y.Y.
      • Tang L.H.
      • Coit D.G.
      • et al.
      MET expression and amplification in patients with localized gastric cancer.
      Trials investigating the efficacy of monoclonal antibodies against hepatocyte growth factor (rilotumumab) and the MET receptor (onartuzumab) were recently reported. Based on the encouraging results of a randomized Phase II trial of rilotumumab in patients with MET-overexpressing gastroesophageal cancer,
      • Iveson T.
      • Donehower R.C.
      • Davidenko I.
      • et al.
      Rilotumumab in combination with epirubicin, cisplatin, and capecitabine as first-line treatment for gastric or oesophagogastric junction adenocarcinoma: an open-label, dose de-escalation phase 1b study and a double-blind, randomised phase 2 study.
      the Phase III RILOMET-1 (Phase III, randomized, double-blind, multicenter, placebo (P)-controlled trial of rilotumumab (R) plus epirubicin, cisplatin and capecitabine (ECX) as first-line therapy in patients with advanced MET-positive gastric or gastroesophageal junction (G/GEJ) cancer) trial was initiated.
      • Cunningham D.
      • Tebbutt N.C.
      • Davidenko I.
      • et al.
      Phase III, randomized, double-blind, multicenter, placebo (P)-controlled trial of rilotumumab (R) plus epirubicin, cisplatin and capecitabine (ECX) as first-line therapy in patients (pts) with advanced MET-positive (pos) gastric or gastroesophageal junction (G/GEJ) cancer: RILOMET-1 study.
      This study randomly assigned patients with untreated advanced MET-positive gastroesophageal cancer to receive ECX with or without rilotumumab. Of approximately 1,500 patients screened, 1,043 patients were considered MET-positive by IHC (≥25% membranous staining) and 600 patients were randomly assigned. Similar to the REAL-3 study, the addition of rilotumumab to chemotherapy had a detrimental effect on OS (9.6 vs 11.5 months; HR = 1.37; 95% CI, 1.06−1.78; P = 0.0016) and the trial was terminated early. Surprisingly, neither MET overexpression by IHC nor MET amplification by FISH was associated with better outcomes in the rilotumumab arm. Further correlative biomarker studies are currently ongoing. The METGastric (A phase III study of onartuzumab plus mFOLFOX6 in patients with metastatic HER2-negative and MET-positive adenocarcinoma of the stomach or gastroesophageal junction) trial investigated the efficacy of onartuzumab, a monoclonal antibody against the MET receptor, in patients with untreated advanced MET-positive gastoesophageal cancer.
      • Shah M.A.
      • Bang Y.-J.
      • Lordick F.
      • et al.
      METGastric: A phase III study of onartuzumab plus mFOLFOX6 in patients with metastatic HER2-negative (HER2-) and MET-positive (MET+) adenocarcinoma of the stomach or gastroesophageal junction (GEC).
      The study was designed to randomly assign approximately 800 patients to receive FOLFOX plus onartuzumab or placebo. However, enrollment stopped early due to negative final results of a randomized Phase II trial of FOLFOX plus onartuzumab.
      • Shah M.A.
      • Cho J.Y.
      • Huat I.T.B.
      • et al.
      Randomized phase II study of FOLFOX +/- MET inhibitor, onartuzumab (O), in advanced gastroesophageal adenocarcinoma (GEC).
      A total of 562 patients were enrolled before the METGastric study closed. For the entire study population, onartuzumab failed to improve outcomes (median OS 11.3 vs 11.0 months; HR = 0.82; P = 0.244). For patients with MET-overexpressing tumors by IHC (2+ and 3+), there was a trend toward improved OS in the onartuzumab arm (11.0 vs 9.7 months; HR = 0.64; P = 0.062). Further analyses to understand the reasons underlying these negative results and identify subgroups that may respond to MET inhibition are needed. In contrast to monoclonal antibodies, promising results were recently reported on a highly selective MET small molecule inhibitor, AMG 337.
      • Kwak E.L.
      • LoRusso P.
      • Hamid O.
      • et al.
      Clinical activity of AMG 337, an oral MET kinase inhibitor, in adult patients (pts) with MET-amplified gastroesophageal junction (GEJ), gastric (G), or esophageal (E) cancer.
      In a first-in-human study presented at the 2015 American Society of Clinical Oncology Gastrointestinal Cancers Symposium, 13 patients with MET-amplified gastroesophageal cancer were enrolled. AMG 337 monotherapy produced a dramatic response in this subset of patients, with 8 patients (62%) achieving partial or complete response. Given these encouraging results, a Phase II study of AMG 337 in MET-amplified gastroesophageal cancer and other solid tumors is planned (ClinicalTrials.gov ID: NCT02016534).

      3.2.5 Antiangiogenic Therapy

      Angiogenesis and the vascular endothelial growth factor (VEGF) pathway play an important role in the pathogenesis of gastroesophageal cancer. Both VEGF-A and VEGF receptor-2 (VEGFR-2) monoclonal antibodies have been investigated in unselected patient populations with metastatic gastroesophageal cancer. After the success of bevacizumab, a monoclonal antibody against VEGF-A, in metastatic colorectal cancer, the AVAGAST (Avastin in Gastric Cancer) study evaluated its activity in advanced gastroesophageal cancer.
      • Ohtsu A.
      • Shah M.A.
      • Van Cutsem E.
      • et al.
      Bevacizumab in combination with chemotherapy as first-line therapy in advanced gastric cancer: a randomized, double-blind, placebo-controlled phase III study.
      In this multicenter, Phase III trial, 774 patients were randomly assigned to receive cisplatin and capecitabine with or without bevacizumab. Although both median PFS (6.7 vs 5.3 months; HR =0.8; 95% CI, 0.68−0.93; P = 0.0037) and overall response rate (46% vs 37.4%; P = 0.0315) were improved with bevacizumab vs placebo, median OS did not differ significantly between the 2 arms (12.1 vs 10.1 months; HR = 0.87; 95% CI, 0.73−1.03; P = 0.1002). Patients with high plasma levels of VEGF-A and low levels of neuropilin, a co-receptor of VEGF-A, derived the greatest benefit from the combination of bevacizumab with chemotherapy.
      • Van Cutsem E.
      • de Haas S.
      • Kang Y.-K.
      • et al.
      Bevacizumab in combination with chemotherapy as first-line therapy in advanced gastric cancer: a biomarker evaluation from the AVAGAST randomized phase III trial.
      In contrast to bevacizumab, the VEGFR-2 antibody ramucirumab has been more effective. Two Phase III trials have evaluated its efficacy in the second-line setting, the first one as monotherapy and the second one in combination with paclitaxel. The REGARD (Ramucirumab monotherapy for previously treated advanced gastric or gastroesophageal junction adenocarcinoma) trial randomly assigned patients who had disease progression after first-line chemotherapy for advanced gastric and gastroesophageal junction adenocarcinoma to receive ramucirumab or placebo.
      • Fuchs C.S.
      • Tomasek J.
      • Yong C.J.
      • et al.
      Ramucirumab monotherapy for previously treated advanced gastric or gastro-oesophageal junction adenocarcinoma (REGARD): an international, randomised, multicentre, placebo-controlled, phase 3 trial.
      Median OS was 5.2 months for the ramucirumab group and 3.8 months for the placebo group (HR = 0.776; 95% CI, 0.603−0.998; P = 0.047). A subsequent study compared the combination of ramucirumab and paclitaxel with paclitaxel as second-line treatment of advanced gastroesophageal adenocarcinoma.
      • Wilke H.
      • Muro K.
      • Van Cutsem E.
      • et al.
      Ramucirumab plus paclitaxel versus placebo plus paclitaxel in patients with previously treated advanced gastric or gastro-oesophageal junction adenocarcinoma (RAINBOW): a double-blind, randomised phase 3 trial.
      The RAINBOW (Ramucirumab plus paclitaxel versus placebo plus paclitaxel in patients with previously treated advanced gastric or gastroesophageal junction adenocarcinoma) study met its primary end point, with a median OS of 9.6 months for the ramucirumab arm vs 7.4 months for the control arm (HR = 0.807; 95% CI, 0.678−0.962; P = 0.0017). Based on these results, ramucirumab is now regarded as a new standard therapy for patients with advanced gastroesophageal adenocarcinoma who have failed prior platinum or 5-fluorouracil chemotherapy. However, as the benefit from VEGFR-2 therapy is relatively small, it is critical to identify biomarkers that will enrich the selection of patients likely to benefit from ramucirumab. Given the positive results of the REGARD and RAINBOW trials, the efficacy of ramucirumab is being investigated in the first-line setting. The first trial comparing the combination of FOLFOX plus ramucirumab with FOLFOX alone in treatment-naïve patients with advanced gastroesophageal adenocarcinoma failed to improve outcomes (median PFS 6.4 vs 6.7 months; HR = 0.98; 95% CI, 0.69−1.37; P = 0.89; and median OS 11.7 vs 11.5 months; HR = 1.08; 95% CI, 0.73−1.58).
      • Yoon H.H.
      • Bendell J.C.
      • Braiteh F.S.
      • et al.
      Ramucirumab (RAM) plus FOLFOX as front-line therapy (Rx) for advanced gastric or esophageal adenocarcinoma (GE-AC): Randomized, double-blind, multicenter phase 2 trial.
      It is important to note that the high discontinuation rate in the ramucirumab arm (48% vs 16% in the placebo arm) may have affected the results of this trial. Additional clinical trials exploring other combinations with ramucirumab are currently ongoing.

      3.3 Genomic Complexity and Heterogeneity

      One of the potential barriers to the success of targeted therapy in gastric and esophageal cancers is their genomic complexity and heterogeneity. Recent genomic studies have reported on the degree of this complexity and highlight the challenges of biomarker assessment. Kim et al
      • Kim J.
      • Fox C.
      • Peng S.
      • et al.
      Preexisting oncogenic events impact trastuzumab sensitivity in ERBB2-amplified gastroesophageal adenocarcinoma.
      investigated the spectrum of baseline oncogenic alterations in HER2-amplified gastroesophageal adenocarcinomas. Of 62 tumors, 42 (62%) had additional co-occurring alterations in potentially targetable genes, such as EGFR, MET, ERBB3, CCNE1, CDK6, CCND1, and PIK3CA. Among these, the most statistically significant secondary alteration was CCNE1 amplification. The authors also assessed the impact of some of these secondary alterations (CCNE1, CDK6, MET amplification, PIK3CA mutation) on the response to lapatinib in vitro. Indeed, these concurrent genomic alterations confer resistance to HER2 inhibition, which can be reversed with combination therapy targeting both HER2 and the secondary driver events. This study emphasizes the need to genomically profile ERBB2-amplified tumors for the presence of additional alterations and suggests that combination of targeted agents may be more effective than HER2-directed monotherapy. Consistent with these observations, Kwak et al
      • Kwak E.L.
      • Ahronian L.G.
      • Siravegna G.
      • et al.
      Molecular heterogeneity and receptor co-amplification drive resistance to targeted therapy in MET-amplified esophagogastric cancer.
      found a high rate of co-occurring oncogenic alterations in a series of MET-amplified gastroesophageal adenocarcinomas. Specifically, 48% (10 of 21) of these tumors harbored co-amplification of either HER2 or EGFR, and that co-amplification was present simultaneously within the same tumor cells. This study also highlights the clinical significance of both the genomic complexity and heterogeneity. In this case series, a patient with HER2 and MET co-amplification was treated with trastuzumab, crizotinib, and paclitaxel and experienced near-complete resolution of her disease. Furthermore, patients with MET-amplified gastroesophageal cancer were found to have striking heterogeneity in MET amplification between the primary tumors and distinct metastatic sites. These patients had a mixed response to MET inhibition and eventually disease progression due to outgrowth of the non-MET−amplified clones. Similar analyses of tumors from patients enrolled in other targeted therapy trials may explain these failures and provide insight into the mechanisms of de novo resistance to these targeted agents.

      3.4 Future of Targeted Therapy Trials in Gastric and Esophageal Adenocarcinoma

      It is now clear that gastroesophageal adenocarcinoma should not be viewed as a single homogeneous entity. Genomic studies have identified multiple potential therapeutic targets, which are present in ≤20% of gastroesophageal cancers. The low frequency of these events poses significant challenges to the design of biomarker-driven trials. Several thousands of patients need to be screened to select the population with the specific genomic alteration. A potential solution is to conduct “basket” trials, where patients with various tumor types that harbor a particular molecular alteration are treated with a drug that targets that driver event. One of the limitations of this trial design is that it is histology-agnostic. However, recent data suggest that the disease-specific context of a genomic alteration plays an important role in the response to targeted therapy. In striking contrast to the dramatic response of BRAF-mutant melanoma to BRAF inhibition, BRAF-mutant colorectal cancers were refractory to these agents.
      • Kopetz S.
      • Desai J.
      • Chan E.
      • et al.
      Phase II Pilot Study of Vemurafenib in Patients With Metastatic BRAF-Mutated Colorectal Cancer.
      ,
      • Corcoran R.B.
      • Atreya C.E.
      • Falchook G.S.
      • et al.
      Combined BRAF and MEK Inhibition With Dabrafenib and Trametinib in BRAF V600-Mutant Colorectal Cancer.
      Another trial design that may prove to be useful for assessing targeted therapies in a more efficient fashion is “umbrella” trial, where patients with one particular tumor type are assigned to different targeted agents according to their tumors’ specific genomic alterations. This trial design allows us to simultaneously test a variety of targeted drugs in biomarker-selected patient cohorts. One such trial in gastroesophageal cancer, the PANGEA (Personalized Antibodies for Gastroesophageal Adenocarcinoma) trial, has been initiated (ClinicalTrials.gov ID: NCT02213289). This study will utilize molecular profiling (both genomic and proteomic analysis) to assign patients with advanced gastroesophageal cancer to different treatment arms, consisting of chemotherapy plus a targeted agent. Clinical trial design should also take into account the genomic complexity and heterogeneity of gastroesophageal cancer. Trials examining the activity of drug combinations will be critical to develop effective therapeutic strategies. In addition, as heterogeneity of targets is common, we need to explore new methods of biomarker assessment, either by performing biopsies of multiple metastatic sites or, more importantly, by identifying circulating biomarkers, such as circulating tumor DNA.

      4. Conclusions

      Gastroesophageal adenocarcinoma is a common and deadly disease. Progress in the treatment of this disease has been slow and outcomes are poor. The advent of new technologies has enabled a molecular classification of these tumors and revealed distinct subgroups with potentially targetable alterations. However, genome-guided therapies have been disappointing thus far. The only biomarker-directed therapy in routine use is trastuzumab as first-line therapy of HER2-positive gastroesophageal cancer, with only modest efficacy. All other molecularly driven trials, including trials evaluating MET and FGFR2 inhibition, have been negative. Not surprisingly, several studies of targeted agents in unselected patient populations have also failed to improve outcomes. It is therefore crucial to understand the reasons for these failures and develop smart trial designs that will allow us to test rational therapeutic approaches.

      Conflicts of Interest

      The author has indicated that she has no conflicts of interest regarding the content of this article.

      Acknowledgments

      Dr. Pectasides’ research is financially supported by the Conquer Cancer Foundation American Society of Clinical Oncology Young Investigator Award, the Debbie’s Dream Foundation−AACR Gastric Cancer Research Fellowship and the Claudia Adams Barr Program for Innovative Cancer Research.

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