Role of the transitional mucosa of the colon in differentiating primary adenocarcinoma from carcinomas metastatic to the colon. An immunohistochemical study.

Differentiation between primary colonic adenocarcinoma arising in flat mucosa and carcinoma metastatic to the colon is often difficult. Examination of the mucosa adjacent to the tumor, the so-called transitional mucosa (TM), may be helpful. The morphologic, ultrastructural, and histochemical characteristics of the TM have been reported previously in detail. In this study the morphologic and immunohistochemical characteristics of the TM have been compared in 18 cases of primary colonic adenocarcinoma and 13 cases of metastasis to the colon. Five immunophenotypic markers were used: carcinoembryonic antigen (CEA), Lewis (x) and (y) blood group antigens, ras oncogene p21, and tumor-associated glycoprotein (TAG-72). Neoplastic transformation of colonic epithelium is associated with altered expression of these antigens. The morphologic and immunohistochemical profile of the TM was similar in both primary colonic adenocarcinomas and metastases to the colon. In some cases the TM adjacent to colonic metastases stained with one or more antibodies while the metastatic tumor was negative. Therefore, in cases where differentiation between primary colonic adenocarcinoma arising in flat mucosa and metastasis is difficult, the use of these reagents, particularly CEA, TAG-72, or ras oncogene p21, may be helpful. The similar immunohistochemical staining pattern of the TM in both primary and metastatic colon lesions supports a reactive, non-neoplastic origin of the TM. Furthermore, expression of these antigens is not limited to neoplastic epithelial cells.