Gastric cancer, a leading cause of cancer-related deaths, is a heterogeneous disease. We aim to establish clinically relevant molecular subtypes that would encompass this heterogeneity and provide useful clinical information. We use gene expression data to describe four molecular subtypes linked to distinct patterns of molecular alterations, disease progression and prognosis. The mesenchymal-like type includes diffuse-subtype tumors with the worst prognosis, the tendency to occur at an earlier age and the highest recurrence frequency (63%) of the four subtypes. Microsatellite-unstable tumors are hyper-mutated intestinal-subtype tumors occurring in the antrum; these have the best overall prognosis and the lowest frequency of recurrence (22%) of the four subtypes. The tumor protein 53 (TP53)-active and TP53-inactive types include patients with intermediate prognosis and recurrence rates (with respect to the other two subtypes), with the TP53-active group showing better prognosis. We describe key molecular alterations in each of the four subtypes using targeted sequencing and genome-wide copy number microarrays. We validate these subtypes in independent cohorts in order to provide a consistent and unified framework for further clinical and preclinical translational research.

Of 458 patients, 228 were randomly assigned to the XP arm and 230 to the XP/XRT/XP arm. Treatment was completed as planned by 75.4% of patients (172 of 228) in the XP arm and 81.7% (188 of 230) in the XP/XRT/XP arm. Overall, the addition of XRT to XP chemotherapy did not significantly prolong disease-free survival (DFS; P = .0862). However, in the subgroup of patients with pathologic lymph node metastasis at the time of surgery (n = 396), patients randomly assigned to the XP/XRT/XP arm experienced superior DFS when compared with those who received XP alone (P = .0365), and the statistical significance was retained at multivariate analysis (estimated hazard ratio, 0.6865; 95% CI, 0.4735 to 0.9952; P = .0471). CONCLUSION The addition of XRT to XP chemotherapy did not significantly reduce recurrence after curative resection and D2 lymph node dissection in gastric cancer. A subsequent trial (ARTIST-II) in patients with lymph node-positive gastric cancer is planned.

In D2-resected GC, both adjuvant chemotherapy and chemoradiotherapy are tolerated and equally beneficial in preventing relapse. Because results suggest a significant DFS effect of chemoradiotherapy in subsets of patients, the ARTIST 2 trial evaluating adjuvant chemotherapy and chemoradiotherapy in patients with node-positive, D2-resected GC is under way.

The VIKTORY (targeted agent eValuation In gastric cancer basket KORea) trial was designed to classify patients with metastatic gastric cancer based on clinical sequencing and focused on eight different biomarker groups (RAS aberration, TP53 mutation, PIK3CA mutation/amplification, MET amplification, MET overexpression, all negative, TSC2 deficient, or RIC-TOR amplification) to assign patients to one of the 10 associated clinical trials in second-line (2L) treatment. Capivasertib (AKT inhibitor), savolitinib (MET inhibitor), selumetinib (MEK inhibitor), adavosertib (WEE1 inhibitor), and vistusertib (TORC inhibitor) were tested with or without chemotherapy. Seven hundred seventy-two patients with gastric cancer were enrolled, and sequencing was successfully achieved in 715 patients (92.6%). When molecular screening was linked to seamless immediate access to parallel matched trials, 14.7% of patients received biomarker-assigned drug treatment. The biomarker-assigned treatment cohort had encouraging response rates and survival when compared with conventional 2L chemotherapy. Circulating tumor (ctDNA) analysis demonstrated good correlation between high MET copy number by ctDNA and response to savolitinib. SIGNIFICANCE:Prospective clinical sequencing revealed that baseline heterogeneity between tumor samples from different patients affected response to biomarker-selected therapies. VIKTORY is the first and largest platform study in gastric cancer and supports both the feasibility of tumor profiling and its clinical utility.

The establishment of better selection criteria for identifying sub-populations that may benefit from treatment is a key aspect of the development and success of targeted therapy. To investigate methods for assessing MET overexpression in gastric cancer, we conducted immunohistochemistry using a new anti-Total MET monoclonal antibody in a single-institution cohort of 495 patients. As antibody is directed against a membranous and/or cytoplasmic epitope, two interpretation methods were used: (1) membranous and cytoplasmic and (2) membranous alone. In selected 120 cases, copy number gain and mRNA expression levels were measured using quantitative real-time PCR. Further in situ hybridization confirmed the presence of MET gene amplification. Among the 495 gastric cancers, simultaneous membranous and cytoplasmic overexpression of MET was found in 108 cases (21.8%) and membranous alone overexpression was observed in 40 cases (8.1%). The highest correlation was observed in membranous and cytoplasmic staining of MET: MET expression scores correlated significantly with high MET mRNA levels (r ¼ 0.465, Po0.0001), increased copy number gain (r ¼ 0.393, P ¼ 0.000002) and amplification of MET gene. Moreover, patients with MET overexpression showed shorter overall survival (HR, 1.781; 95% CI, 1.324-2.395; Po0.001) and disease-free survival (HR, 1.765; 95% CI, 1.227-2.541; P ¼ 0.002) compared with patients without MET overexpression. However, membranous overexpression of MET did not highly correlate with mRNA level (r ¼ 0.274, P ¼ 0.002), copy number gain or survival (P40.05). We developed highly correlating interpretation methods of MET immunohistochemistry in gastric carcinomas. MET overexpression is an independent prognostic factor and could be a potential target and predictor of benefit for targeted therapy with MET inhibitors. Recently, the addition of trastuzumab to standard cytotoxic chemotherapy demonstrated significant survival benefit in HER2-positive gastric carcinomas. 2 Nevertheless, HER2 is positive in only a small portion of gastric cancer patients (7-20%); thus, more precise molecular segmentation is urgently needed. 3 One potential target in gastric cancer was identified as MET proto-oncogene (hepatocyte growth factor receptor) in preclinical studies. 1,4 As mutations in the kinase domain of MET gene are almost lacking in gastric carcinomas, 5 its

clinicaltrials.gov Identifier: NCT01725789.

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Endoscopic resection might not be inferior to surgery with respect to OS in patients with EGC lesions that meet the absolute or expanded criteria. However, DFS, RFS, and metachronous RFS might be lower after endoscopic resection than after surgery.