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

The immunohistochemical distribution of inhibin-a in formalin-fixed, paraff in-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-alpha was strongly and diffusely expressed in s yncyriotrophoblast. Implantation site intermediate trophoblast in normal an d exaggerated placental sites was either negative or only weakly and focall y positive for inhibin-cu. With increasing gestational age, the staining in tensity and distribution of inhibin-a decreased in syncytiotrophoblast incr eased in the implantation site intermediate trophoblast. Chorionic-type int ermediate trophoblast, present in the chorion laeve of the term placenta, w as weakly but diffusely positive for inhibin-alpha. Cytotrophoblast remaine d negative for inhibin-alpha throughout gestation. In trophoblastic lesions , inhibin-a immunoreactivity was detected in all 17 hydatidiform moles (7 c omplete and 10 partial), 32 placental site nodules, 23 placental site troph oblastic tumors, 15 epithelioid trophoblastic tumors, and 16 choriocarcinom as. Inhibin-alpha immunoreactivity was confined to the syncytiotrophoblast in hydatidiform moles and choriocarcinoma. As with the normal placenta, inh ibin-alpha was not detected in cytotrophoblast. To evaluate the utility of inhibin-alpha in the differential diagnosis of gestational trophoblastic le sions, we tested 32 squamous cell carcinoma of the cervix, 11 low-grade end ometrial stromal sarcomas, 12 endometrial (7 well differentiated and 5 mode rately differentiated) carcinomas, 7 epithelioid leiomyomas, and 10 leiomyo sarcomas for the expression of inhibin-a. None of these lesions was positiv e. These data indicate that inhibin-si is expressed by all populations of t rophoblast except cytotrophoblast and in all,gestational trophoblastic lesi ons. Accordingly, immunohistochemical detection of inhibin-alpha is useful in the differential diagnosis of gestational trophoblastic lesions.