How are neuroendocrine tumors classified?
- The spectrum ranges from well-differentiated neuroendocrine tumors (carcinoid tumors) to poorly differentiated (small cell carcinomas) and large cell neuroendocrine carcinomas.
- The common site of involvement is the rectum, followed by the cecum and sigmoid colon.
- The histologic characteristics are similar to those described in the small intestine section. These are sporadic tumors. The malignancy rate of 11% to 14% has been calculated for rectal carcinoids.
- The malignancy criteria include size greater than 2 cm, invasion into muscularis propria, and increased mitoses.
