Myoid gonadal stromal tumor: a distinct testicular tumor with peritubular myoid cell differentiation

We report a distinct, primary testicular tumor with peritubular myoid cell differentiation. A 25-year-old man developed a well-circumscribed testicular tumor composed of cytologically bland spindled cells, which were strongly and diffusely positive for desmin, smooth muscle actin, muscle-specific actin, and smooth muscle myosin. In addition, S-100 was diffusely positive, and cytokeratin (CK5/6 and AE1/3) was focally positive. Calretinin, inhibin, and CD34 were all negative. This pattern of immunoreactivity was very similar to the normal adjacent peritubular myoid cells. Follow-up after radical orchiectomy showed benign behavior. We found reports of 6 similar intratesticular tumors demonstrating peritubular myoid cell-like differentiation and having favorable outcome. We believe that the myoid gonadal stromal tumor is a rare, yet distinct, testicular tumor separate from leiomyoma and deserves recognition.