Neuroendocrine differentiation in "poorly differentiated" colon carcinomas.

The diagnosis of "poorly differentiated" carcinoma was made in 47 of 683 colon cancers on the basis of conventional light microscopy which showed poorly defined glands, solid architecture or variable admixtures thereof. Samples from 44 of these 47 tumors were assessed by immunohistochemical analysis for the presence of neuroendocrine (NE) antigens. Paraffin sections were immunostained with antibodies to NSE, chromogranin, serotonin, VIP, substance P and somatostatin. Additional sections were also stained with monoclonal antibody (Mab) A-80 that recognizes a glycoprotein related to exocrine (EX) differentiation. Based on our findings, the tumors were phenotypically reclassified as follows: I) pure EX (n = 8), II) pure NE (n = 4), III) mixed EX-NE carcinomas (n = 23), and IV) predominantly EX carcinomas with occasional NE cells (n = 9). Survival among groups II and III appeared to be less than group I and survival in group IV was significantly less than group I. Survival among the four pure NE (group II) and 11 predominantly NE mixed carcinomas (group III) taken together was significantly less than the pure EX carcinomas. This study indicates: 1) The incidence of NE differentiation in tumors of the colon and rectum is higher than previously believed. 2) The poorly differentiated colon carcinomas comprise four distinct groups: pure EX, pure NE, mixed EX-NE carcinomas, and predominantly EX carcinomas with a NE cell subpopulation. 3) The presence of NE differentiation or of a NE cell subpopulation in colon carcinoma appears to be associated with a poorer prognosis.