Two subtypes in colorectal mucinous carcinoma in relation to microsatellite instability

Although some investigators have attempted to divide colorectal mucinous adenocarcinoma into two entities, there have been few reports describing microsatellite instability of each subtype. In this study, we elucidated the clinicopathological features of subtypes in mucinous carcinoma, especially the relationship between microsatellite instability and each subtype.

The present study included 33 patients with mucinous colorectal cancer. The 33 patients were classified into two groups; the papillotubular type group (n = 22) and the mucocellular type group (n = 11). The clinicopathological aspects and microsatellite instability were examined.

Significant differences were found between the papillotubular type group and the mucocellular type group regarding the following findings such as lymphatic invasion, lymph node metastasis, peritoneal metastasis, and Dukes stage. The mucocellular type group had 2 cases with high-frequency microsatellite instability, 7 cases with low-frequency microsatellite instability and 2 cases with microsatellite stability. Conversely, the papillotubular type group included 12 cases with high-frequency microsatellite instability, 3 cases with low-frequency microsatellite instability and 7 cases with microsatellite stability. The ratio of cases with high-frequency microsatellite instability in the mucocellular type group (18.1%) was significantly lower than that of the papillotubular type group (54.5%) (P = 0.0463). The 5-year survival rate of the mucocellular type group (29.1%) was significantly lower than that of the papillotubular type group (70.3%) (P = 0.0282).

Colorectal mucinous carcinoma needs to be classified into two groups, papillotubular type and mucocellular type, because of significant differences in microsatellite instability and patients' survival.