A Leydig Cell Tumour in a Cat: Histological and Immunohistochemical Findings

A 13-year-old intact male cat was submitted to castration after the finding of the enlargement of the right testis during the clinical visit. Macroscopically, a nodule of 2？cm of diameter was observed on the cut surface of the enlarged testis. Histologically, the nodule was composed by polyhedral to elongated cells with a large, eosinophilic, and vacuolated cytoplasm and small, round, and dark nuclei. These cells were arranged in acinar structures and solid sheets. The tumour was diagnosed as a Leydig cell tumour. Immunohistochemical analysis revealed that neoplastic cells were vimentin, calretinin, and melan-A positive, whereas a lack of immunoreactivity to cytokeratins confirmed the diagnosis. To our knowledge, this is the first description of a feline Leydig cells tumour without any concurrent testicular neoplasm or in a nonretained testis. 1. Introduction Leydig cell tumours are neoplasms originating from the interstitial Leydig cells of the testis. These tumours are common in dogs and more rarely reported in other species [1]. In cats, few cases of testicular tumors have been, up now, described [2, 3] including some Leydig cell tumours located in retained testis, in castrated cats, or with a concurrent testicular neoplasm [4–7]. Here, we describe for the first time a case of feline leydigioma occurring in a noncastrated cat and without testicular retention. 2. Case Presentation At the clinical exam, a 13-year-old intact European shorthair male cat showed the increase in volume and firmness of the right testis, while the left one was atrophic. Both were normally located into the scrotum. Ultrasonographic investigations allowed to identify an hypoechogenic nodule of 2？cm of diameter in the enlarged testis. The cat did not present behavioral alterations as aggressiveness, feminization, or inappropriate urination. According to the owner’s will, the cat was submitted to surgery to remove both the gonads. On gross evaluation, the mass of the right testis was yellow to brown-colored and firm and elastic at the palpation. The neoplasm was well circumscribed and clearly demarcated from the healthy testis. Tissue samples were fixed in 10% neutral buffered formalin and processed by routine methods for histological investigation. Four m thick sections were cut and stained with hematoxylin and eosin for microscopic examination. Further tissue sections were prepared for immunohistochemical staining. Immunohistochemistry was performed with the biotin-streptavidin-peroxidase method with primary antibodies against human pan-cytokeratins (CK), vimentin, melan-A, and