High risk of multiple gastric cancers in Japanese individuals with Lynch syndrome

Abstract Aim Lynch syndrome (LS) is a dominantly inherited syndrome characterized by an increased risk for LS associated tumors such as colorectal cancer (CRC) and gastric cancer (GC). However, the clinical benefit of surveillance for GC remains unclear while it has already been recommended for CRC. This study aimed to elucidate the clinical features of GC in Japanese individuals with LS, and the risk of developing multiple GCs to build regional‐tailored surveillance programs in LS patients with GC. Methods Data on Japanese individuals with LS were retrospectively collected from a single institution. The clinical features of GC, including the cumulative risk of multiple GCs, were analyzed. Results Among 96 individuals with LS ( MLH1 / MSH2 / MSH6 , 75:20:1), 32 GC lesions were detected in 15 individuals with LS (male/female, 11:4). The median age at initial GC diagnosis was 52.7 y (range: 28–71). Histological examination revealed a predominance of intestinal type (19/24: 87.5%). Moreover, the majority of the GC lesions (82%) were determined to have high‐frequency of microsatellite instability. The cumulative risk of individuals with LS developing GC at 70 y was 31.3% ( MLH1 36.1%, MSH2 18.0%). Notably, the cumulative risk of individuals with LS developing metachronous and/or synchronous GCs at 0, 10 and 20 y after initial diagnosis of GC was 26.7%, 40.7%, and 59.4%, respectively. Conclusion Due to a higher risk of developing multiple GCs, intensive surveillance might be especially recommended for Japanese individuals with LS associated initial GC.