Calretinin: a valuable marker of normal and neoplastic Leydig cells of the testis.

Sex cord-stromal tumors represent approximately 4% of all testicular neoplasms. Leydig cell tumor (LCT) is the most common entity, followed by Sertoli cell tumor (SCT). Leydig cell tumor histologic diagnosis is usually easy, but occasional forms of LCT could mimic others neoplasms, especially SCT or variants of yolk sac tumor. The aim of this study was to investigate calretinin expression in LCT and SCT of the testis. We evaluated calretinin reactivity in formalin-fixed, paraffin-embedded sections of 10 LCT, three SCT, five Leydig cell hyperplasia, two Sertoli cell adenomas, eight seminomatous tumors, five nonseminomatous germ cell tumors (mixed tumor), one adenomatoid tumor, and two normal testes using a standard immunohistochemical technique with a microwave-mediated epitope retrieval. All cases of LCT showed a positive staining that was diffuse and intense, constantly cytoplasmic, and sometimes nuclear. A positive strong and diffuse cytoplasmic and sometimes nuclear staining was also observed in Leydig cell hyperplasia and in normal Leydig cells. No staining was seen in two of three cases of SCT, and focal staining was observed in the third case. Only rare scattered cells were weakly immunostained in the Sertoli cell nodules. Seminomatous and nonseminomatous germ cell tumors were negative. Calretinin is an interesting marker of normal and neoplastic Leydig cells of the testis and may be of value in the diagnosis of atypical LCT.