Immunohistochemical localization of inhibin-α in the placenta and gestational trophoblastic lesions

The immunohistochemical distribution of inhibin-α in formalin-fixed, paraffin-embedded tissues was evaluated in placentas (2 to 40 weeks of gestation), implantation sites, and a variety of trophoblastic lesions. In the first trimester placenta, inhibin-α was strongly and diffusely expressed in syncytiotrophoblast. Implantation site intermediate trophoblast in normal and exaggerated placental sites was either negative or only weakly and focally positive for inhibin-α. With increasing gestational age, the staining intensity and distribution of inhibin-α decreased in syncytiotrophoblast but increased in the implantation site intermediate trophoblast. Chorionic-type intermediate trophoblast, present in the chorion laeve of the term placenta, was weakly but diffusely positive for inhibin- α. Cytotrophoblast remained negative for inhibin-α throughout gestation. In trophoblastic lesions, inhibin-α immunoreactivity was detected in all 17 hydatidiform moles (7 complete and 10 partial), 32 placental site nodules, 23 placental site trophoblastic tumors, 15 epithelioid trophoblastic tumors, and 16 choriocarcinomas. Inhibin-α immunoreactivity was confined to the syncytiotrophoblast in hydatidiform moles and choriocarcinoma. As with the normal placenta, inhibin-α was not detected in cytotrophoblast. To evaluate the utility of inhibin-α in the differential diagnosis of gestational trophoblastic lesions, we tested 32 squamous cell carcinoma of the cervix, 11 low-grade endometrial stromal sarcomas, 12 endometrial (7 well differentiated and 5 moderately differentiated) carcinomas, 7 epithelioid leiomyomas, and 10 leiomyosarcomas for the expression of inhibin-α. None of these lesions was positive. These data indicate that inhibin-α is expressed by all populations of trophoblast except cytotrophoblast and in all gestational trophoblastic lesions. Accordingly, immunohistochemical detection of inhibin-α is useful in the differential diagnosis of gestational trophoblastic lesions.