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

Background: 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.

Case description: We present the case of an 83-year-old female who presented to the emergency room with a 4-month history of cramping abdominal pain associated with nausea, emesis, and decreased appetite with associated weight loss. Diagnostic imaging demonstrated a bowel obstruction secondary to a mass in the cecum and she underwent an exploratory laparotomy with right hemicolectomy. She was found to have a collision carcinoma of the cecum and ileocecal valve containing both mucinous adenocarcinoma and neuroendocrine tumor. Diagnosis was confirmed post-operatively with pathologic examination and immunohistochemical testing.

Conclusions: Diagnosing collision tumors upon patient presentation is exceedingly difficult as the symptoms are often identical to other neoplasms of the GI tract and vary based on location of the tumor. It is thought that the true prevalence of collision tumors is underestimated due to history of changing nomenclature, unclear diagnostic criteria, unreported cases, and unrecognized cases. Furthermore, new advances in immunohistochemical evaluation have allowed for better characterization of these neoplasms. With clarification regarding nomenclature, diagnostic criteria and expanding awareness, it is our hope that this leads to an increase in reported cases, allowing for an expanded discussion and resulting growth of literature and further studies. Further knowledge regarding the pathogenesis, treatment, and prognosis is needed.