The roles of CAM5.2 and caldesmon IHC stains in challenge of diagnosing adenoma, intramucosal carcinoma, and invasive adenocarcinoma on colon biopsies

Making a distinction between adenoma, intramucosal carcinoma, and invasive carcinoma on small biopsies of colon polypoid lesions can occasionally pose a challenge to pathologists. In our study, we aimed to assess the staining patterns and utilities of the two immunohistochemical stains CAM5.2 and caldesmon in helping with this endeavor. Routinely processed colon polyps biopsies’ specimens from 57 patients with CAM5.2 and caldesmon ordered were reviewed by three pathologists. We found CAM5.2 and caldesmon to be very useful in classifying these colon polypoid lesions. CAM5.2 highlighted single cells and cribriform architecture. Caldesmon stained the lamina propria, the smooth muscle, and the desmoplastic stroma surrounding invasive tumor in colonic submucosa with different morphologic characteristics. First, in the lamina propria, caldesmon was mostly negative with faint brown lines surrounding glands and small vessels. Second, in the smooth muscle of muscularis mucosa, caldesmon stained the cytoplasm lightly with solid and diffuse pattern. Third, in the desmoplastic area of the submucosa, caldesmon stained the cytoplasm strongly with a clear space or groove seen at the middle of the cytoplasm (tram-tracking appearance). We described our findings in this study with hope that more pathologists will utilize these two stains in their common practice to reliably diagnose invasion by colon carcinoma.