Primary Prostatic Alveolar Rhabdomyosarcoma in Adult, a Diagnostic Pitfall: Report of an Extremely Rare Tumor

IntroductionPrimary sarcoma of the prostate is extremely rare and accounts for less than 1% of all prostatic malignancies. Alveolar rhabdomyosarcoma arising from the prostate in an adult man is exceedingly rare. Establishing a correct diagnosis is often challenging in a prostatic core biopsy.Patient presentationA 30-year-old man presented to the emergency department after a period of acute urinary retention. Clinical examination revealed an indurated prostatic mass. Serum prostate-specific antigen level was normal. Imaging work-up showed pelvic lymph node and vertebral metastases. A malignant pleural effusion was noted. Transrectal ultrasound-guided core biopsy from the prostate revealed a cellular malignant neoplasm with small round tumor cells arranged in nests and sheets. Initial diagnosis of prostatic adenocarcinoma, Gleason score 5 + 5, grade group 5 was made. Immunohistochemical work-up showed positive skeletal muscle markers (desmin, myogenin and MYOD1) with negative keratin (AE1/AE3), NKX3.1, synaptophysin, chromogranin. CD56 showed patchy positivity. A revised diagnosis of primary alveolar rhabdomyosarcoma was established. The patient succumbed to the disease soon after the diagnosis.DiscussionPrimary alveolar rhabdomyosarcoma of the adult prostate has been rarely reported. The tumor has an aggressive clinical course with dismal prognosis. The diagnosis can be challenging as the histomorphology closely resembles poorly differentiated carcinoma, non-Hodgkin lymphoma, small cell carcinoma and other small round cell sarcomas. Aberrant immunohistochemical expression causes diagnostic dilemma. The treatment protocol and adjuvant drugs differ significantly from prostatic adenocarcinoma or small cell carcinoma, necessitating an accurate histological diagnosis for appropriate patient management. A molecular work-up can be useful in challenging specimens.