Rare Collision Tumor of the Biliary Tract.

Malignancies of the gallbladder are uncommon in the developed world. Collision tumors are also extremely rare neoplastic phenomena. Given their scarcity, there are no guidelines for treatment, and prognosis is based on the more aggressive tumor type. We present a patient with a collision tumor consisting of signet-ring cholangiocarcinoma and large-cell neuroendocrine gallbladder carcinoma of the biliary tract, and we review the literature pertaining to biliary tract collision tumors and their management.