TRANSFORMATION OF OVARIAN DYSGERMINOMA TO YOLK-SAC TUMOR - EVIDENCE FOR A HISTOGENETIC CONTINUUM

Dysgerminoma has traditionally been considered an end-stage neoplasm w ithout potential for further differentiation. Although there have been several reports of transformation of testicular seminoma to yolk sac tumor, a similar event has not been previously reported in dysgerminom a of the ovary. Three cases of ovarian germ cell tumor (two pure dysge rminomas and one mixed germ cell tumor with dysgerminoma and yolk sac components) that revealed histologic changes compatible with early tra nsformation to yolk sac tumor are described. In general, the areas of transformation were located at the periphery of the tumor lobules whic h otherwise had features of typical dysgerminoma. They were characteri zed by the presence of microcysts and small glandular structures, whic h though not readily identified on H&E became more evident with stains for keratins, a-fetoprotein, and blood group-related antigen. The sma ll size and focal nature of change, and the apparent transition favor the interpretation that this change represents transformation rather t han admixture of two germ cell components, The relationship of dysgerm inoma to the solid variant of yolk sac tumor is discussed and an alter nate histogenetic scheme in which dysgerminoma represents the stage of earliest differentiation from which other non dysgerminomatous tumors may arise is presented. Although previously proposed for testicular g erm cell neoplasia, this scheme has not yet been applied to their ovar ian counterparts,