Background: Although testicular tumors commonly develop in the genital tract of dogs, only few studies have reported about metastatic testicular tumors in dogs to date. Therefore, the present study aimed to describe the gross, histopathological, and immunohistochemical findings in a dog with metastatic interstitial cell tumor.Case: A 6-year-old male Beagle underwent clinical examination due to enlargement of the left testicle and nodules in the skin of the left inguinal region and of the scrotum. The left testicle was cryptorchid (inguinal), and the right testicle was intrascrotal. Both testicles and affected skin fragments were surgically removed. The right testicle was normal in size and did not exhibit gross changes. However, the left testicular parenchyma had been completely replaced by a firm, grayish-to-white neoplastic mass with an irregular surface. The inguinal and scrotal skin fragments were thickened by the neoplastic masses. Histologically, the left testicular parenchyma was completely obliterated by a neoplastic mass consisting of round-to-oval and polygonal cells. The neoplastic cells generally had abundant eosinophilic cytoplasm with indistinct cell limits. The nuclei were round and small, with aggregated chromatin. However, some cells exhibited high degrees of atypia and pleomorphism and large nuclei with granular chromatin. Mitotic figures were observed at high frequencies of up to 11 per high-power field (400×). The mass in the left testicle was diagnosed as malignant interstitial cell tumor. The sections of the inguinal skin and scrotum presented with neoplastic cells similar to those observed in the left testicle, which is consistent with the metastasis of the malignant testicular interstitial cell tumor. On the basis of necropsy, multiple cutaneous and subcutaneous nodules were randomly distributed throughout the body, primarily in the prepuce, head, and limbs. Histological evaluations of the skin nodules, internal iliac lymph nodes, and abdominal skeletal muscles also revealed metastases of the testicular interstitial cell tumor.Discussion: The histopathological findings associated with the immunohistochemical results observed in the present case helped in establishing the diagnosis of malignant interstitial cell tumor. Regarding the histological evaluations, although most neoplastic cells exhibited appearances that are characteristic of Leydig cells, several features indicative of malignancy were also observed. In dogs, malignant interstitial cell tumors are rare, and multiple organ metastases have been described. Among the immunohistochemical markers that were examined (calretinin, vimentin, cytokeratin, placental alkaline phosphatase, and octamer-binding transcription factor 3/4), only vimentin staining produced a positive result. In one study, the antibody against vimentin stained both normal Sertoli and Leydig cells and tumors arising from these cells, but not seminomas, which is an important differential diagnosis in the case described in this study. The negativity for placental alkaline phosphatase also allowed to rule out seminoma in the differential diagnosis of the primary tumor. The skin sections (distant metastases) were negative for T and B lymphocytes and macrophages, thereby ruling out possible differential diagnoses, such as lymphomas or histiocytic tumors, among the cutaneous neoplasms. Therefore, this case report described a malignant testicular interstitial cell tumor with an uncommon disseminated pattern of metastases to the skin in a dog.
Immunohistochemical characteristics of renomedullary interstitial cell tumor: a study of 41 tumors with emphasis on differential diagnosis of mesenchymal neoplasms
