Histology in mixed germ cell tumors. Is there a favorite pairing?

Purpose: Mixed germ cell tumors account for approximately 30% to 50% of testicular tumors. To our knowledge a systematic review with statistical analysis of the associations of histological subtypes in mixed germ cell tumors has not been done previously. It was our impression that such associations exist. Delineating concordant histological types may provide insight into the ontogeny of testicular tumors and also have important clinical implications. Materials and Methods: We retrospectively reviewed the testis cancer data base at our institution. The primary tumor of orchiectomy specimens was examined in 2,589 patients. Of these patients mixed histology was noted in 1,765 (68.2%). ORs were calculated for all possible combinations of teratoma, embryonal carcinoma, yolk sac tumor, choriocarcinoma and seminoma. In addition, we evaluated the association of various histological types with teratoma at post-chemotherapy retroperitoneal lymph node dissection. Results: Of 10 possible combinations of histological types in the primary tumor, positive correlations were noted in 4. The strongest correlation was found between teratoma and yolk sac tumor (OR 2.58, p <0.001). Teratoma or yolk sac tumor in the testis was associated with teratoma in the pathology specimen at post-chemotherapy retroperitoneal lymph node dissection. Conclusions: The strongest associations of histological subtypes in mixed germ cell tumors were seen between yolk sac tumor and teratoma. Similar associations are seen in late relapse and in some cases of prepubertal tumors. Further study of these associations may prove valuable in understanding the biology and clinical behavior of germ cell tumors.