Frequent microsatellite instability in papillary and solid-type, poorly differentiated adenocarcinomas of the stomach

Microsatellite instability (MSI) has been observed in 8-39 % of sporadic gastric cancers. However, despite numerous reports indicating a significant relationship between intestinal-type histology and MSI, detailed correlation between histological subtypes and MSI remains obscure. The purpose of the present study is to clarify the relationship between histological subtype and microsatellite status in gastric carcinomas.

Microsatellite status was examined for 464 consecutive gastric carcinomas from 420 patients as well as histological subtypes and other clinicopathological findings.

MSI was observed in 82 carcinomas (17.7 %), and the greatest proportions were observed in solid-type, poorly differentiated adenocarcinoma (43.0 %) and papillary adenocarcinoma (32.5 %), both being significantly higher than those of other subtypes. The proportion increased with advancing age (0 % at 51-64 years, 8.5 % at 65-74 years, 18.4 % at 75-84 years, 35.3 % at 85-96 years). Compared with microsatellite-stable carcinomas, microsatellite-unstable carcinomas were significantly related with older age, female gender, antral location, and predominant papillary adenocarcinoma and solid-type, poorly differentiated adenocarcinoma. Poorly differentiated type carcinoma was significantly less frequent than differentiated type in microsatellite-unstable cancer at the early stage, whereas no significant difference existed at the advanced stage.

These results suggest that there are specific histological subtypes with highly frequent MSI and that gastric carcinoma with MSI originates from differentiated-type carcinomas, indicating histological diversity during tumor growth.