Fluorescence In Situ Hybridization for the X and Y Chromosome Centromeres Helps Differentiate Between Gestational and Nongestational Choriocarcinoma in Clinically Ambiguous Cases.

CONTEXT.—: Gestational choriocarcinoma usually presents during the reproductive years, typically within 1 year of pregnancy, although presentation remote from pregnancy also occurs and may cause confusion with other tumors, including choriocarcinoma of germ cell origin and somatic carcinomas with choriocarcinomatous differentiation. It is important to separate these tumors for treatment and prognostic reasons. OBJECTIVE.—: To assess the utility of fluorescence in situ hybridization for the X and Y chromosome centromeres in determining the gestational origin of clinically ambiguous extrauterine choriocarcinomas in women. DESIGN.—: A review of female patients with extrauterine choriocarcinomas who had no evidence of prior gestational trophoblastic disease was performed. Samples were analyzed by fluorescence in situ hybridization for the X and Y chromosome centromeres using standard methodologies. RESULTS.—: Five cases met the criteria, all of which displayed trophoblastic cells and necrosis. Three cases (60%) had Y chromosomes by fluorescence in situ hybridization, which confirmed gestational origin. Although the 2 cases without a Y chromosome would ordinarily require molecular genotyping for paternal genetic material to establish gestational origin, in one of these cases a subsequent recurrence of yolk sac tumor allowed confirmation of its mediastinal origin. CONCLUSIONS.—: Fluorescence in situ hybridization for detection of the X and Y chromosome centromeres is an effective screening test for gestational choriocarcinoma. It provided a definitive diagnosis of metastatic gestational choriocarcinoma in 3 of 5 potential cases that lacked a clinical history of gestational trophoblastic disease. An additional benefit is that more laboratories have the capability to perform fluorescence in situ hybridization than can perform molecular genotyping for definitive diagnosis.