Collision tumor of the cecum and ileocecal valve composed of mucinous adenocarcinoma and neuroendocrine tumor: a case report

Collision tumors of the gastrointestinal (GI) tract are thought to be uncommon, with those of the colon being rare with very few cases reported in current literature. There are three proposed theories regarding the etiology of collision tumors currently, including the "double primaries", the "biclonal malignant transformation", and the "tumor-to-tumor carcinogenesis" theories. Prognosis of collision tumors remains unclear. To our knowledge, this is the fifth case of a collision carcinoma involving the cecum and ileocecal valve and the first report of a collision carcinoma including both mucinous adenocarcinoma and neuroendocrine tumor of the cecum and the ileocecal valve. The aim of this paper is to explore the history of collision tumors and associated nomenclature, defined diagnostic criteria, and proposed theories for etiology in addition to patient presentation, approach to diagnosis, treatment options, and prognosis.