Ovarian choriocarcinoma: a difficult diagnosis of an unusual tumor and a review of the hook effect.

Ovarian choriocarcinoma is difficult to diagnose in the reproductive-age patient. A case of nongestational ovarian choriocarcinoma is discussed which presented like a molar pregnancy initially. Because of falsely low beta-hCG values (283 mIU/L) caused by the high-dose "hook effect" in the double antibody immunoassay system, however, a diagnosis of ectopic pregnancy was entertained. At laparotomy, a large necrotic ovarian choriocarcinoma was found along with large theca lutein cysts. The hook effect may mislead the clinician, and it is important to recognize this effect to avoid misdiagnosis.