Treatment of Rectal Neuroendocrine Tumors

In general, rectal neuroendocrine (carcinoid) tumors often present as very small, isolated lesions.[1] The TNM (tumor, node, metastasis) system is used for rectal neuroendocrine tumors, but size appears to be one of the best estimates of recurrence. Rectal neuroendocrine tumors should be evaluated by endoscopic ultrasonography (EUS) or rectal magnetic resonance imaging (MRI). Tumors smaller than 1 cm can be safely removed by endoscopic excision.[2-5] Excised specimens should be examined histologically to exclude muscularis invasion.[2,6-8]. A report about the patients with rectal carcinoid tumors in the Surveillance, Epidemiology, and End Results (SEER) Program database demonstrated that the 5-year survival rate for patients with stage I carcinoid tumors was 97%.[9]

For patients with tumors that are larger than 2 cm or that have invasion of the muscularis as seen by EUS or MRI, surgical resection with abdominoperineal resection (APR) or low anterior resection (LAR) is recommended because of the high rate of nodal metastases and risk of distant metastatic disease. In the report from the SEER database, patients with stage II or III rectal carcinoid tumors had 5-year survival rates of 84% and 20%, respectively.[9] In a report from the National Cancer Database, among 3,287 patients with rectal carcinoid tumors, the 5-year survival rates for patients with stage II or III disease were 87.3% and 35.5%, respectively.[10]

There is considerable debate about whether local excision or rectal resection (i.e., APR or LAR) is needed for tumors that measure 1 cm to 2 cm. Although it may be possible to recognize tumors with particular atypia and high mitotic index before embarking on the more radical surgery, the presence of muscularis invasion or regional metastases generally supports rectal resection. In a multicenter series of 100 patients who underwent anterior resection for rectal carcinoid tumors, the rate of nodal metastases for patients with tumors between 1 cm and 2 cm was 31%.[11] In this series, tumor size larger than 1 cm and lymphovascular invasion were the two strongest predictors of lymph node metastases. In patients with distant metastases, prognosis is generally poor, with an overall 5-year survival rate of approximately 30%.[12]