Gastrointestinal carcinoids and colorectal cancers: is it a paracrine effect?

BACKGROUND: Carcinoid tumors are uncommon neuroendocrine tumors that account for less than 1% of gastrointestinal tract malignancies. They have a reported incidence of 1.3 per 100,000. Small bowel carcinoids are the commonest and have the highest incidence of associated second primary malignancies, followed by appendiceal and colorectal carcinoids. The most common second primary malignancy is colorectal adenocarcinoma. CASE SERIES: We report a series of 11 patients observed in the period 2006-2011 with primary gastrointestinal tract cancers and synchronous carcinoids discovered incidentally by the histopathologist in the resected primary cancer specimen. RESULTS: In all patients with synchronous carcinoids and colorectal adenocarcinoma there was a pattern of similar embryonic visceral origin. Is this a paracrine effect from biological peptides produced by the carcinoids?