Small cell neuroendocrine carcinoma of the colon and rectum: clinical, histologic, and ultrastructural study and immunohistochemical comparison with cloacogenic carcinoma.

In an effort to provide immunocytochemical data that would be useful in distinguishing between small cell epithelial tumors of the anorectal region, 10 cases of neuroendocrine small cell colorectal carcinoma (NSCCC) and five cases of cloacogenic carcinoma (CC) were studied with antibodies to cytokeratin, epithelial membrane antigen (EMA), chromogranin, blood group isoantigens (BGI), carcinoembryonic antigen (CEA), Leu-M1, Leu-7, leukocyte common antigen (LCA), S-100 protein, neurofilaments (NF), neuron-specific enolase (NSE), serotonin, and 14 neuropeptides. The diagnoses for all 15 tumors were verified ultrastructurally. Among the antigenic determinants considered, reactivity for low- and medium-molecular-weight cytokeratin, EMA, NSE, and NF was seen in the majority of NSCCCs, whereas the CCs were positive for all cytokeratin classes, BGI, EMA, and CEA. In addition, Leu-M1, Leu-7, and chromogranin were each expressed in three cases of NSCCC. None of the other antisera yielded positive results in tumors of either type. All 10 patients with NSCCC died of their tumors within 11 months of clinical presentation, while four of the five CCs proved fatal, with an average survival of 28 months. One of the patients with CC was free of disease 31 months after diagnosis. These data suggest that an immunocytochemical panel, consisting of antibodies to high-molecular-weight cytokeratin, BGI, CEA, NSE, and NF (and possibly Leu-7 and chromogranin as well), is capable of distinguishing between NSCCC and CC in problematic cases. Although tumors of both types are aggressive, it is possible that the survival statistics for both may be improved through more accurate diagnostic classification.