Small-cell undifferentiated carcinoma of the rectosigmoid colon.

We describe three patients with small-cell undifferentiated carcinoma of the rectosigmoid colon. Though there was a wide range of patient age, history, and gross presentation of the malignancy, there was overlap in the histopathologic appearance and the biological behavior of the tumor. All three cases had liver involvement at the time of diagnosis. Despite multidrug chemotherapy, two patients died within a year of diagnosis, and the third patient had progressive disease. Ultrastructurally, all cases had membrane-bound dense-core granules, however, there was considerable variation of size and number of granules among the tumors, as well as other forms of endodermal differentiation. Whether small-cell undifferentiated carcinoma presents as a small focus within a neoplastic polyp or as a large primary tumor, the therapy must include a systemic aggressive protocol.