The expression of carcinoma-associated antigens and blood-group-related antigens in rectal carcinoids.

The immunohistochemical expression of blood-group substances and carcinoma-associated antigens were compared in rectal carcinoids and adenocarcinomas. Rectal carcinoid tumors, in contrast to rectal carcinomas, were consistently negative for CEA, gastrointestinal cancer antigen GICA (or CA 19-9), and carcinoma-associated antigen CA-50 (except in one case where less than 10 percent of the cells expressed CA-50). The carcinoids and rectal carcinomas extensively expressed blood-group substance A, B, and H, Lewis B antigen, and difucosylated carbohydrate antigens (DFCA). Thus, rectal carcinoids and adenocarcinomas possess both similar and different tumor antigen profiles. The occurrence of discrepant antigen determinants may be used in the differential diagnosis of these two types of tumors. The coexpression of blood-group substance A, B, and H, Lewis B antigen, and DFCA is consistent with the opinion that both rectal carcinomas and carcinoids have a common entoderm origin, but carcinoids are considered to rise from the endocrine-differentiated and the adenocarcinomas from the nonendocrine-differentiated enterocytes.