Molecular and pathological analyses of gastric stump cancer by next-generation sequencing and immunohistochemistry.

Gastric stump cancer (GSC) has distinct clinicopathological characteristics from primary gastric cancer. However, the detailed molecular and pathological characteristics of GSC remain to be clarified because of its rarity. In this study, a set of tissue microarrays from 89 GSC patients was analysed by immunohistochemistry and in situ hybridisation. Programmed death ligand 1 (PD-L1) was expressed in 98.9% of tumour-infiltrating immune cells (TIICs) and 6.7% of tumour cells (TCs). Epstein-Barr virus (EBV) was detected in 18 patients (20.2%). Overexpression of human epidermal growth factor receptor 2 and deficiency of mismatch repair (MMR) protein expression were observed in 5.6% and 1.1% of cases, respectively. Moreover, we used next-generation sequencing to determine the gene mutation profiles of a subset of the 50 most recent patients. The most frequently mutated genes were TP53 (42.0%) followed by SMAD4 (18.0%) and PTEN (16.0%), all of which are tumour suppressor genes. A high frequency of PD-L1 expression in TIICs and a high EBV infection rate suggest immune checkpoint inhibitors for treatment of GSC despite a relatively low frequency of deficient MMR gene expression. Other molecular characteristics such as PTEN and SMAD4 mutations might be considered to develop new treatment strategies.