Canine testicular tumors: two types of seminomas can be differentiated by immunohistochemistry

BACKGROUND: Testicular tumors are the most common genital neoplasms in male dogs, with Leydig cell tumors (LCT), seminomas (SEM), and Sertoli cell tumors (SCT) the most common forms. Human SEM are classified as classical (CSEM) or spermatocytic (SSEM). Intratubular germ cell neoplasia of undifferentiated origin (IGCNU) is another form of human testicular tumor. The aim of this study was to verify that CSEM/SSEM classification is valid in dogs and confirm the existence of canine IGCNU. RESULTS: Testicular tumors were found in 46% of dogs at necropsy and accounted for 7% of tumors biopsied. The median age of dogs with tumors at necropsy was 10.16 years; median age at positive biopsy was 10.24 years. The most common tumors, in decreasing order, were LCT, mixed tumors, SEM and SCT at necropsy, and SEM, SCT, mixed tumors, LCT, peripheral nerve sheath tumor, and teratoma in the biopsy group. IGCNU was found in 3% of testicles at necropsy and in 3% of biopsy samples. Two dogs had testicular tumor metastasis. Expression of c-KIT was most common in SEM and seminomatous components of mixed tumors. PLAP was mostly expressed in IGCNU, SEM, teratoma, and some mixed tumors. Cytokeratin was mainly expressed in SCT. CD30 expression was low in both groups. CONCLUSIONS: The high tumor incidence at necropsy can be attributed to older age. Tumor incidence in biopsy samples, dog age, and histological classification were consistent with previous studies. The higher incidence of SEM and SCT in the biopsy group probably resulted from the obvious clinical expression of these tumor types. The low incidence of metastasis confirmed the predominance of benign tumors. Low CD30 expression confirmed the low incidence of testicular embryonal carcinoma. Cytokeratin helps differentiate stromal tumors, especially SCT, from germ cell tumors. Histology and c-KIT and PLAP expression indicate that IGCNU exists in dogs. Expression of c-KIT and PLAP confirmed that CSEM and SSEM classification is valid in dogs.