Immunohistochemical differentiation of clear-cell carcinoma of the female genital tract and endodermal sinus tumor with the use of alpha-fetoprotein and Leu-M1.

The morphologic differentiation between clear-cell carcinoma and endodermal sinus tumors is difficult at times. To improve the accuracy of the diagnosis, the authors studied nine ovarian and eight vaginal clear-cell carcinomas and seven endodermal sinus tumors of the ovary by immunohistochemical methods with the use of antibodies to alpha-fetoprotein and Leu-M1. Sixteen (94.1%) of the 17 clear-cell carcinomas and two (28.5%) of the seven endodermal sinus tumors reacted for Leu-M1, whereas six (85.7%) of the seven endodermal sinus tumors and three (17.6%) of the 17 clear-cell carcinomas stained for alpha-fetoprotein. Three clear-cell carcinomas and two endodermal sinus tumors showed immunoreactivity for both markers. No reactivity for either of these markers was present in one endodermal sinus tumor and one clear-cell carcinoma. All 13 tumors that stained only for Leu-M1 proved to be clear-cell carcinomas, and the four that reacted exclusively for alpha-fetoprotein were endodermal sinus tumors. Therefore, the authors concluded that positive immunostaining for Leu-M1 and negative immunostaining for alpha-fetoprotein support the differential diagnosis of clear-cell carcinoma, whereas a positive reaction for alpha-fetoprotein and a negative reaction for Leu-M1 favor a diagnosis of endodermal sinus tumor. However, positive or negative staining for both markers appears to have no diagnostic value.