Comparative molecular subtypes of index and metachronous gastric adenocarcinomas: a study of 42 Korean patients.

To date, there have been no studies comparing the molecular subtypes of Index gastric cancers (IGCs) and metachronous gastric cancers (MGCs). We evaluated a cohort of 42 patients with 43 IGCs and 45 MGCs. Molecular subtyping was performed by immunohistochemistry of mismatch repair (MMR) proteins, E-cadherin, p53, and Epstein-Barr virus- (EBV-) in situ hybridization (ISH). Gastric adenocarcinomas were classified into 5 subtypes: EBV-associated, MMR deficient (MMRD), E-cadherin aberrant, p53-aberrant [p53(+)], and p53 non-aberrant [p53(neg)]. All IGCs had been successfully treated by either surgery (19%) or endoscopic resection (81%). The mean interval between IGCs and MGCs was 85 months. Among the IGCs, EBV-associated, MMRD, E-cadherin-aberrant, p53(+), and p53(neg) molecular subtypes represented 2 (5%), 4 (9%), 2 (5%), 21 (49%), and 14 (32%) of the cases, respectively. Two cases had concomitant p53(+) and aberrant E-cadherin molecular subtypes. Among metachronous cancers, EBV-associated, MMRD, E-cadherin-aberrant, p53(+), and p53(neg) molecular subtypes represented 3 (7%), 11 (24%), 0 (0%), 22 (49%), and 9 (20%) cases. Concomitant p53(+) was observed in 1 EBV-associated and 2 MMRD MGCs. Although, there was no significant difference in the frequency of most molecular subtypes in IGCs and MGCs, the number of MMRD gastric cancers more than doubled in the MGC group. Half of the MGCs had a divergent molecular subtype compared to that of the IGCs. Notably, the interval between the development of IGCs and MGCs was significantly longer in patients with divergent molecular subtypes (P = 0.010). All 4 patients with MMRD IGC developed MMRD MGCs. Although the concept of mucosal field cancerization may explain the matching molecular subtypes in early-developing MGCs, the presence of divergent subtypes in late-occurring MGCs suggests a shift in the carcinogenic mechanism affecting the residual mucosa possibly related to Helicobacter pylori eradication.