Hepatoid malignancy of unknown origin-a diagnostic conundrum: review of literature and case report of collision with adenocarcinoma

Conclusion: The most likely explanation in our case is that the hepatoid tumor either originated from microscopic remnant ovarian tissue left behind or primarily from the peritoneum. With no evidence of yolk sac component within the colonic tumor or in the draining lymphatics, this essentially excludes the commonly observed metastatic dedifferentiation (opisthoplasia) of adenocarcinoma to primitive forms (also known as combination tumors). Based on analysis of various factors, including tumor behavior and response to chemotherapy, we conclude that our case was a hepatoid variant of yolk sac tumor presenting in an elderly woman with carcinomatosis. This unusual presentation of two entirely different primary malignancies in close proximity is defined as “collision tumor”. This is the first reported case of collision tumors involving dual colonic and primary peritoneal hepatoid-YST. Identifying the exact type still remains to be the most challenging aspect in the diagnosis of hepatoid tumors.