Phyllodes tumor of the prostate: long-term followup study of 23 cases.

PURPOSE: Phyllodes tumor of the prostate is a rare neoplasm of uncertain malignant potential. We studied a large series of phyllodes tumors to define the combination of histological features that are most useful for predicting patient outcome.

MATERIALS AND METHODS: A total of 23 cases were obtained from our collective files from 1973 to 2002, and numerous clinical and pathological features were evaluated. A review of the reported cases of phyllodes tumor of the prostate was done.

RESULTS: Patient age was 25 to 86 years (mean 55) and they usually presented with urinary obstructive symptoms and hematuria. The diagnosis was made in 18 tumors by transurethral resection, in 2 by enucleation, in 1 by tumor resection and in 2 by prostatectomy. We analyzed 5 histological features, including cellularity (scale of 1 to 3), cytologic atypia (scale of 1 to 3), the number of mitotic figures per 10 high power fields, the stroma-to-epithelium ratio (low or high) and necrosis (present or absent). This combination of features revealed that 14 cases were low grade phyllodes tumor, 7 were intermediate grade and 2 were high grade with the high grade cases characterized by increased cellularity, severe cytological atypia, more than 5 mitotic figures per 10 high power fields and a high stroma-to-epithelium ratio, indicating stromal overgrowth. Immunohistochemical studies of 8 tumors revealed consistent, intense cytoplasmic immunoreactivity in stromal cells for vimentin and actin, in luminal epithelial cells for prostate specific antigen, prostatic acid phosphatase and broad-spectrum keratin AE1/AE3, and in basal cells for high molecular weight keratin 34beta-E12. Recurrence was seen in 7 of 14 low grade tumors (50%) and in 1 patient low grade sarcoma emerged with subsequent distant metastases 14 years after initial diagnosis following 5 recurrences. Recurrence was seen in 6 of 7 intermediate grade tumors and low grade sarcoma emerged with subsequent abdominal wall metastases in 1 patient 11 years after initial diagnosis following 3 recurrences. The phyllodes tumor recurred in each patient with high grade tumors with a time to first recurrence of 6 and 0.2 years, respectively. Distant metastases developed in these 2 patients.

CONCLUSIONS: Histological grading of prostatic phyllodes tumors is predictive of short-term outcome based on the combination of stromal cellularity, cytological atypia, number of mitotic figures and the stroma-to-epithelium ratio. However, these tumors usually recur after transurethral prostatic resection and they are often locally aggressive with time. The emergence of overt sarcoma and metastatic disease is more frequent than previously recognized. Complete resection at initial diagnosis appears to be indicated.