A clinicopathologic, histologic, and immunohistochemical study of mixed germ cell-stromal tumors of the testis in 16 dogs.

In a review of 262 neoplasms in 225 dogs, 18 tumors in 16 dogs were mixed germ cell-stromal tumors containing intimately admixed germ cells and Sertoli cells in tubular structures of various sizes. Seven of the 18 neoplasms were predominantly composed of germ cells, and 11 were predominantly composed of Sertoli cells. In 15 neoplasms, the germ cells were more anaplastic than the Sertoli cells, and in three neoplasms, both cell types were anaplastic. Five of the seven mixed-cell tumors with predominantly germ cells had germ cells infiltrating the adjoining tissues. Immunocytochemical studies of all 18 mixed-cell tumors, testes from five clinically normal dogs, six seminomas, and six Sertoli cell tumors revealed that neuron specific enolase (NSE) and vimentin were useful in demonstrating the dual population of the mixed cell tumors by differential staining of the germ cells and Sertoli cells. Half of the tumors stained differentially with desmin. In the normal testes, seminomas, and Sertoli cell tumors, parallel staining of germ cells and Sertoli cells by NSE and vimentin was seen, but only the appropriate tissues stained with desmin. The mixed-cell tumors in this study had morphologic features in common with mixed germ cell-sex cord stromal tumors and gonadoblastomas of human beings; clinically, they had more in common with the former. These mixed cell tumors in dogs should be classified separately.