Classic and "Dissecting" Gonadoblastoma in a Phenotypic Girl With a 46, XX Peripheral Karyotype and No Evidence of a Disorder of Sex Development.

Herein, we report a case of a 9-yr-old girl who had a 46, XX peripheral karyotype and apparent developmentally normal ovaries. She presented with abdominal pain and a right adnexal mass. No clinical or pathologic evidence of gonadal dysgenesis or undifferentiated gonadal tissue was detected. She underwent right salpingo-oophorectomy with rupture of the tumor at the time of operation due to recent adnexal torsion. The original pathologic diagnosis was gonadoblastoma and mixed germ cell tumor. Most significantly in our study, we identified a rare and novel pathway for the development of malignant mixed germ cell tumor from gonadoblastoma in the absence of identifiable dysgerminoma. The histologically identifiable steps of progression in our case were as follows: (1) residual islands of classic gonadoblastoma, (2) overgrowth by "dissecting" gonadoblastoma composed of transformed germ cells with clear cytoplasm and sex cord elements surrounded by a basement membrane, (3) stromal infiltration by dedifferentiated germ cells with loss of basement membrane, (4) formation of malignant mixed germ cell tumor. The dedifferentiated areas were composed of anaplastic germ cells with amphophilic cytoplasm that gradually replaced the sex cord elements by clonal expansion. Both the original transformed and the anaplastic germ cell components strongly expressed OCT4. We believe that the mixed germ cell tumor arose from the dedifferentiated germ cell component through neoplastic progression. This premise suggests that the germ cell component of "dissecting" gonadoblastoma rarely undergoes anaplastic change in the absence of transition to germinoma and can be the direct precursor of mixed germ cell tumor.