[Neuroendocrine neoplasms of the appendix and colorectum]

Appropriate diagnosis and treatment of neuroendocrine neoplasms (NENs) of the appendix and colorectum requires a detailed knowledge of their proper classification according to the updated WHO and TNM systems. The WHO classification distinguishes well differentiated NEN, the neuroendocrine tumors (G1 and G2 NETs), from the poorly differentiated carcinomas (G3 NECs). While NETs are common in the appendix and rectum, NECs occur predominantly in the colon. G1 appendiceal and rectal NETs of 1 cm in size or below that do not invade either the muscular wall or vessels bear almost no metastatic risk and can be treated by appendectomy or endoscopic resection. G2 appendiceal and rectal NETs larger than 1 cm in size in combination with other risk factors have an increased risk of metastasis and need to be treated more aggressively. NECs of the colon usually require chemotherapy in addition to resection. Today, most patients with NETs of the appendix and rectum have an excellent prognosis when these diagnostic and therapeutic guidelines are borne in mind.