APUD system neoplasms in renal transplant patients

Apudomas are uncommon neoplasms composed of neuroendocrine cells. They include carcinoid tumors, islet cell tumors, and small cell lung carcinoma. We found six cases of apudomas in a series of 1028 renal transplants from three medical centers (0.58%). One of these had been reported in 1976. The cases included a carcinoid tumor of a Meckel's diverticulum discovered and removed prior to transplantation, with no evidence of recurrence 9 years later. A small cell lung carcinoma was discovered 40 months after renal transplantation, with a fatal outcome 6 months later. Four clinically occult apudomas were found at autopsy, including one gastric and one bronchial carcinoid tumor, one multicentric pancreatic islet cell neoplasm, and one case of multiple ileal carcinoids. With the exception of the small cell lung cancer, none of the apudomas was clinically significant, and none was associated with carcinoid or other paraneoplastic syndrome. These cases illustrate the difficulty of diagnosis of apudomas in patients with renal failure and the usually benign nature of these tumors despite the administration of potent immunosuppressive agents.