Leiomyosarcoma of the prostate. Report of 23 cases

Leiomyosarcoma of the prostate is a rare neoplasm that accounts for less than 0.1% of prostate malignancies. Previous reports of this neoplasm consisted of single case studies or small series, often combined with cases of rhabdomyosarcoma. The relationship of prognosis with histologic and immunohistochemical findings has not, to the authors' knowledge, been described in a large series of cases, and the efficacy of various treatments is uncertain.

The authors undertook a clinicopathologic study of all cases of prostate leiomyosarcoma observed at their institution from 1929 to 1994. Twenty-three cases were retrieved from the files of the Department of Pathology, Mayo Clinic (Rochester, MN), and clinical follow-up was available for 14. Immunohistochemical studies, including actin, desmin, S-100 protein, keratin, and vimentin were performed for 18 cases.

Patients ranged in age from 41 to 78 years, with a mean of 61 years. Presenting symptoms included urinary obstruction (100%), perineal pain (25%), burning on ejaculation (7%), and weight loss (7%). The neoplasms ranged from 3.3 to 21 cm (mean, 9 cm) in greatest dimension and were often associated with necrosis. Seven tumors were Grade 2, 10 Grade 3 and 6 Grade 4 (Broders' grading system; scale, 1-4). Mitotic figure counts varied from 2 to 24 per 10 high power fields. Fifteen of 15 (100%) cases were immunoreactive for vimentin, 10 of 16 (63%) were immunoreactive for actin, and 3 of 15 (20%) were weakly reactive for desmin. Keratin expression was observed in 4 of 15 cases (27%), and S-100 protein was negative in all cases. Treatment varied, and usually included a combination of radiation therapy, chemotherapy, and radical prostatectomy or cystoprostatecomy. Follow-up ranged from 2 to 72 months, with a mean of 19 months. Ten patients died from tumor 3 to 72 months (mean, 22 months) after diagnosis. Four patients were alive, including three with residual tumor and one without evidence of tumor at 2, 4, 30, and 4.5 months, respectively. Local recurrence occurred in 10 of 11 patients, including 5 who had gross residual tumor present after surgery. Metastases developed up to 40 months after surgery (mean, 10.3 months), and most frequently involved the lungs.

These findings indicate that prostate leiomyosarcoma has a varied histologic appearance ranging from spindled cell neoplasm reminiscent of smooth muscle to pleomorphic sarcoma. Epithelioid features may be present. Most tumors are immunoreactive with antibodies to vimentin and actin, and reactivity with antikeratin antibodies does not exclude the diagnosis of leiomyosarcoma. Prostate leiomyosarcoma has a poor prognosis, although the length of survival is variable. Radical surgery was the treatment of choice in the current series, but complete excision was difficult in most cases and did not result in cure.