Impact of adjuvant treatment according to gastric cancer molecular subtypes.

Abstract

e15513 Background: The four subtypes of gastric adenocarcinoma (GC) identified by the Cancer Genome Atlas project (TCGA) have different molecular signatures and prognosis. Several centers have tried to classify GC using immunohistochemistry (IHC) and in situ hybridization (ISH), examining the tumors according to Epstein–Barr virus (EBV) status, microsatellite instability (MSI), aberrant E-cadherin expression and TP53 status. Here we aim to verify the impact of adjuvant/perioperative chemotherapy (ACT/PCT) or adjuvant chemoradiation (CRT) according to the molecular subtypes profile. Methods: We retrospectively reviewed all GC patients who underwent gastrectomy and D2-lymphadenectomy at our institution from a prospective collected medical database. Deficient DNA mismatch repair (dMMR), E-cadherin and p53 were evaluated by IHC for determining the MSI, genomically stable (GS) and chromosomal instability (CIN, with and without p53 aberrant) subtypes, respectively. EBV positivity was detected by ISH. Results: Among the 178 stage II/III patients included, 67 had surgery alone, 47 received ACT/PCT and 64 CRT. 16 had aberrant E-cadherin (GS, 9%), 33 dMMR (MSI, 18.5%), 74 aberrant p53 expression (CIN p53-aberrant, 41.6%), 104 normal p53 expression (CIN p53-normal, 58.4%) and 18 EBV-positivity (EBV, 10.1%). Two or more altered status were present in GC of 16 patients. When analyzed independently, Kaplan-Meier survival analysis showed that EBV, dMMR, CIN p53-normal and GS subtypes did not obtain any benefit of ACT/PCT or CRT in disease free survival (DFS) (p = 0.71; p = 0.33; p = 0.41; p = 0.21, respectively). Meantime, those treatments impact positively in DFS for EBV-negative, proficient MMR and non-GS (p = 0.01; p = 0.007; p = 0.01). CIN subtype with p53 aberrant obtained most benefit for ACT/PCT or CRT (p < 0.001). Conclusions: In accordance with other studies we achieved no benefit for adjuvant chemotherapy in patients with EBV, dMMR and GS GC subtypes. Patients with p53 aberrant expression had greater benefit for ACT/PCT or CRT. This simple method of classification can potentially help to tailor adjuvant treatment.