Pseudosarcomatous fibromyxoid tumor of the urinary bladder and prostate: immunohistochemical, ultrastructural, and DNA flow cytometric analyses of nine cases.

Pseudosarcomatous fibromyxoid tumor of the genitourinary tract is a rare pathologic entity of hitherto unknown etiology that, because of the cellular pleomorphism and the infiltrative nature of the lesion, may be mistakenly diagnosed as sarcomatoid carcinoma or sarcoma. We retrospectively studied nine pseudosarcomatous fibromyxoid tumors involving the bladder and prostate to define characteristic parameters that may allow for accurate diagnosis. The study patients included four men and five women with a mean age of 48.7 years. Histologic analysis revealed myxoid lesions with a proliferation of spindle fibroblastic cells in a background of granulation tissue-type vascularity and inflammatory cells. Mitoses were infrequent and no atypical forms were found. Immunostaining was positive for vimentin and smooth muscle actin, and negative for S-100 protein, desmin, myoglobin, and keratin. Ultrastructurally, the lesion displayed fibroblastic and myofibroblastic cell features. Flow cytometric DNA content analysis revealed uniform DNA diploidy and a low S-phase fraction. All patients were alive and well with no evidence of disease after a mean follow-up of 4.8 years. In contrast, the sarcomatoid carcinomas and sarcomas of the urinary bladder and prostate that were used as controls occurred in older patients and had more frequent mitoses with atypical forms, tumor-type necrosis, and different immunostaining profiles; they were preponderantly aneuploid or diploid with high S-phase fraction. Awareness of the clinicopathologic and biologic characteristics of these lesions is necessary to ensure their accurate diagnosis and to prevent unnecessary radical therapy.