TROPHOBLASTIC-TYPE TUMORS

Choriocarcinoma occurs very rarely as a pure neoplasm; much more often it is a component of a mixed germ cell tumor. Microscopic examination shows patterns similar to those encountered in uterine choriocarcinomas but rarely there is a monophasic pattern (36). The tumors stain immunohistochemically for hCG, placental lactogen (hPL) and various placental proteins. One testicular tumor indistinguishable from the placental site trophoblastic tumor of the uterus has been described in the testis of a child (36). It is important that choriocarcinoma be distinguished from seminoma or embryonal carcinoma with syncytiotrophoblast giant cells. In those instances there is not the admixture of cytotrophoblast with syncytiotrophoblast that is usually seen in choriocarcinoma, even allowing for the fact that some examples of the latter have a less classically formed biphasic pattern than some others. In seminomas and embryonal carcinomas the cells adjacent to the giant cells are typical seminoma or embryonal carcinoma cells. A pattern of embryonal carcinoma that may be misinterpreted as choriocarcinoma is that described many years ago as the appliqué pattern in which cells that are probably degenerative at the periphery of better preserved cells and applied against them sometimes may superficially suggest the biphasic pattern of choriocarcinoma.