Invasive papillary adenocarcinoma of the colon.

Colonic adenocarcinomas are among the most common type of tumors. In this report, we present the morphologic, immunohistochemical, and microsatellite findings of 2 cases with a distinct invasive papillary component. Both tumors arose from polyps in middle-aged patients, followed an aggressive course, and showed a superficial adenomatous component. The immunohistochemical stains showed that the tumor cells were negative for p27 and p53; both tumors were microsatellite stable, that is, with no microsatellite instability in the 6 markers studied, and there was no loss of the mismatch repair proteins hMSH2 or hMLH1. These findings suggest that these tumors follow the tumor-suppressor pathway and represent an aggressive subtype of colonic adenocarcinoma.