Differentiated Rhabdomyomatous Tumor in a Therapy-Naïve Testicular Germ Cell Tumor.

Sarcomatous transformation in testicular germ cell tumors is rare and most commonly associated with post-chemotherapy teratoma. Rhabdomyomatous differentiation is particularly uncommon and typically identified in retroperitoneal lymph node dissection (RPLND) specimens rather than within the primary testicular tumor. We report a unique case of a therapy-naïve 23-year-old male presenting with syncope, dyspnea, abdominal symptoms, and a large right testicular mass. Imaging demonstrated a 12 cm testicular tumor with pulmonary masses suspicious for metastasis. Radical orchiectomy revealed a post-pubertal teratoma containing a predominant (70-80%) differentiated rhabdomyomatous tumor, without mitotic activity, necrosis, or primitive sarcomatous elements. Rare foci of choriocarcinoma were also present. Subsequent jejunal and lung biopsies confirmed metastatic choriocarcinoma. This case represents a rare presentation of a differentiated rhabdomyomatous tumor identified within a primary orchiectomy specimen prior to chemotherapy. Recognition of this rare morphology is clinically relevant, as cytodifferentiated rhabdomyomatous tissue may behave differently from true rhabdomyosarcoma. This report expands the spectrum of testicular germ cell tumor differentiation and contributes to the limited literature regarding sarcomatous evolution in genitourinary malignancy.