PD‐L1 expression in gastric and gastroesophageal junction cancer patients treated with perioperative chemotherapy

Abstract Background and Objectives The incidence, predictive, and prognostic impact of programmed cell death (PD‐L1) expression in gastric (GC) and gastroesophageal junction tumors (GEJC) treated with perioperative chemotherapy is poorly understood. We aimed to assess PD‐L1 expression by immunohistochemistry (IHC) in both pre and posttreatment specimens evaluating its impact on pathological response and survival outcomes. Methods Retrospective cohort of patients with GC and GEJ tumors treated in a single western cancer center between 2007 and 2017. PD‐L1 expression was assessed by IHC before and after neoadjuvant chemotherapy, in surgical samples, and reported as combined positive score (CPS). CPS > 1% was tested for its association with pathological response and overall survival (OS). Results We were able to assess PD‐L1 expression in at least one tissue sample from 155 subjects. PD‐L1 positivity rate was 20%. In 74 paired samples, a 21% discordance between PD‐L1 expression in biopsy sample and surgical specimen was observed. With a median follow‐up period of 60.3 months, 5‐years disease‐free survival was 60.5% with a median OS not reached. PD‐L1 expression was neither associated with pathological response or survival outcomes. Conclusions PD‐L1 expression in the setting of locally advanced GC tumors was relatively low and can vary considering the tissue sample analyzed. This expression had no association with survival or pathological response in this population.