Collision tumor in form of primary adenocarcinoma and neuroendocrine carcinoma of the duodenum

Collision tumor is a rare phenomenon characterized by coexistence of completely distinct and independent tumors at the same body location. Collision tumors have been reported in different sites. However, they are extremely uncommon in the duodenum. We report the case of a 52-year old man with a collision tumor in the third portion of the duodenum with two distinct tumors of primary adenocarcinoma and neuroendocrine carcinoma, and both tumors coexisting within a single metastatic lymph node. Immunohistochemistry studies were performed to conclude that this was a case of collision cancer. To the best of our knowledge, this is the first collision tumor case reported to date at this location, and the first report of lymph node with a collision metastasis from a collision tumor. Such tumor is very rare and may thus provide diagnostic challenges. This report also provides a review of other cases on duodenal collision tumors.