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.