Which Rectal Neuroendocrine Tumors are Dangerous?

In this study of 309 rectal neuroendocrine tumors (NETs), often called rectal carcinoids in the past, endoscopic factors were studied to understand their association with advanced tumors (defined as tumor invading the muscularis propia or with lymph node or distant metastases). A scoring system was generated based on a training set of about two-thirds of the lesions and was validated in the remaining third.

Overall, about two-thirds of the lesions were <1 cm in size, and 20% were 1 to 2 cm. Almost none of the lesions <1 cm in size had advanced disease. In the 1- to 2-cm size range, lesions that were semi-pedunculated, flat, or fungating in shape, or had depression or ulceration on the surface, were more likely to be advanced at diagnosis.