Extraocular muscle metastasis 16 years following primary prostate carcinoma

An 83-year-old man with a history of localized prostate carcinoma treated 16 years prior with transurethral partial prostatectomy and radioactive seed implants presented with a 2-month history of right globe proptosis. Computed tomography demonstrated a right medial rectus mass. Serum prostate specific antigen (PSA) level was normal. Tumor biopsy revealed poorly differentiated carcinoma with diffuse staining of tumor cells with PSA and prostatic acid phosphatase. This case demonstrates that prostate carcinoma may metastasize to an extraocular muscle many years after treatment of the primary tumor and may not be accompanied by elevated serum PSA. Immunohistochemical stains are helpful in establishing the diagnosis.