Microcarcinoid arising in patients with long-standing ulcerative colitis: histological analysis.

Some case reports of neuroendocrine tumors and neuroendocrine carcinoma associated with ulcerative colitis (UC) have been published. Most neuroendocrine tumor cases are small lesions corresponding to microcarcinoids (MCs). However, published case reports have presented findings of MCs as single-case reports. Thus, the frequency of MCs is still unclear. In this study, we described the clinical and morphological features of 14 cases of UC-associated MCs and estimated the frequency of MCs. Consecutive patients with UC who underwent complete removal of the large intestine were assessed, and 135 patients were selected. Of the 135 cases, 14 cases (10.4%) in which MC lesions were observed histologically were classified as the MC group, and the remaining 121 cases were classified as the control group. Seven cases in the MC group (50%) exhibited colitic cancer. No cases in either group had distinct carcinoid tumors. All MC lesions were located in the rectum, and the sizes ranged from 0.1 to 5.5 mm. Eight cases (57%) had multiple MC lesions. The frequency of MCs in UC was estimated to be 10.4%. Most cases of MC were quite unlikely to develop into clinically distinct carcinoid tumors. Thus, when MC lesions remain microscopic, they may not represent true neoplasms, which require immediate surgical resection. Because MC often arose in cases with UC complicated by dysplasia or cancer, patients with UC whose rectal biopsies reveal MC may be at high risk of colitic cancer.