Metastatic prostate carcinoma presenting as a gluteal soft tissue mass

Metastatic lesions from prostate adenocarcinoma to the bone and lymph nodes and less frequently to the lungs, pleura, liver and adrenal glands are well documented. The presence of soft tissue metastases from a prostate adenocarcinoma is extremely rare. We report a case of a 56-year-old male who presented with a 2-year history of a painless buttock mass. MRI showed a well-defined, right gluteal intermuscular soft tissue mass and multifocal hypointense lesions of the pelvic bones and appendicular skeleton suggestive of secondary metastatic disease. Tru-cut biopsy of the gluteal mass demonstrated metastatic adenocarcinoma. Further workup showed an elevated prostate-specific antigen, and acinar adenocarcinoma of the prostate was confirmed on transrectal biopsy of the prostate. Androgen deprivation therapy with long-acting three monthly goserelin and short-term cover with bicalutamide was initiated as was systemic taxane-based chemotherapy. He has shown an excellent PSA response and remains asymptomatic with complete resolution of the size of the gluteal metastasis at the most recent follow-up 9 months later.