PURPOSE: Our goal was to define the incidence of neuroendocrine carcinomas of the colon and rectum, the patterns of neuroendocrine expression, and the cellular subtype within neuroendocrine tumors. We attempted to determine whether differences in neuroendocrine expression or specific cell type influenced survival. METHODS: Over a ten-year period, 988 patients had resections for colorectal cancer. Using immunohistochemical staining methods specific for neuroendocrine markers, 39 (3.9 percent) neuroendocrine cancers were identified retrospectively. Tumors were also stained with monoclonal antibody A-80 which is specific for exocrine differentiation. In this way we were able to determine the extent of neuroendocrine differentiation such as pure neuroendocrine, predominant neuroendocrine, and equal neuroendocrine-exocrine expression. RESULTS: Average patient age was 65.5 (range, 28-89) years; there were 25 males and 14 females. Nineteen tumors were located in the right colon, 11 in the left, and 9 were in the rectum. Three histopathologic patterns were identified: pure neuroendocrine (n = 11), predominantly neuroendocrine (n 17), and cancers with equal exocrine and neuroendocrine differentiation (n = 7). Three cellular subtypes were seen: small-cell (n 15), intermediate-cell (n = 15), and well-differentiated neuroendocrine cancers (n = 5). There was one Dukes A cancer, 7 Dukes B, 16 Dukes C, and 15 patients had metastases to distant sites at the time of diagnosis. As a group, neuroendocrine tumors have a poor prognosis: six-month survival was 58 percent, three-year survival was 15 percent, and five-year survival was 6 percent. Survival statistically correlated with tumor stage (P = 0.01) but not with age, sex, tumor location, histopathologic pattern, or neuroendocrine subtypes. Median survival for pure neuroendocrine carcinomas was seven months and for predominantly neuroendocrine carcinomas was five months. Tumors with equal neuroendocrine and exocrine differentiation had a median survival of 22 months (P = 0.3). Small-cell neuroendocrine carcinomas had a median survival of five months, intermediate-cell had 11 months, and well-differentiated had a median survival of 22 months (P = 0.1). CONCLUSIONS: Neuroendocrine differentiation is found in at least 3.9 percent of colon and rectal cancers. Many of these tumors were initially diagnosed as ''carcinoids,'' the diagnosis was changed to ''neuroendocrine carcinoma'' after immunohistochemical staining. Overall survival is poor especially for small-cell and pure neuroendocrine carcinomas.
