Colonic and Rectal carcinoids
What is a neuroendocrine tumor of the colon or rectum?
Carcinoid tumors of the colon are extremely rare tumors, comprising < 11 percent of all carcinoid tumors and only 1 percent of colonic neoplasms. Typically, carcinoid tumors of the colon present in the sixth to seventh decade of life during evaluation for anorexia, abdominal pain, and unintentional weight loss. Data from several series demonstrate that colonic carcinoids tumors are diagnosed usually late in the course of the disease, and the average size of these tumors was approximately 5 cm at diagnosis. Additionally, at diagnosis, approximately two-thirds of patients have local nodal or distant metastases, resulting in an overall 5-year survival rate of 25% to 41%.
Rectal carcinoids are usually asymptomatic and are discovered incidentally during proctoscopy, sigmoidoscopy, or digital rectal examination. Patients who do have symptoms typically present with rectal pain, bleeding, or constipation. Though these neoplasms represent only 1.3% of all rectal tumors, the true incidence of rectal carcinoids appears to be on the rise due to recent advances in endoscopic technology. Like carcinoids of the small bowel and colon, these tumors are thought to arise from the epithelial endocrine cells; however, unlike these neoplasms, rectal carcinoids contain glucagon and glicentin-related peptides, rather than serotonin. Development of the typical carcinoid syndrome is rare. Interestingly, the size of rectal carcinoids correlates closely with the aggressiveness of the tumor and metastatic potential. Recent series have shown that tumors smaller than 1 cm rarely metastasize, while lymph node and liver metastases are seen in up to 70% of cases in which the primary tumor exceeds 2 cm. Overall 5-year survival rates from the SEER database for localized, regional, or distant disease spread beyond the rectum and rectosigmoid junction over a ten year period were 90, 49, and 26%, respectively.