Prostatic stromal tumor of uncertain malignant potential: a clinicopathologic study of two cases and review of the literature

Prostatic stromal tumor of uncertain malignant potential (STUMP) is rare tumor of the specialized prostatic stroma origin that encompasses a broad spectrum of histologic patterns and clinical behavior. Herein, we aimed to retrospectively review 2 cases of STUMP at our institution with a comprehensive discussion of its distinctive clinicopathologic features as well as the board spectrums of differential diagnosis. The first patient was a 49-year-old man who presented with lower urinary tract symptoms and the sensation of incomplete emptying of the bladder that had persisted for several months. The PSA value was 1.5 ng/ml. Transrectal ultrasound (TURS) of the prostate revealed an enlarged prostate with a mixed echogenic lesion in the peripheral zone. Laparoscopic radical prostatectomy with pelvic lymph node dissection was performed and pathologic examination showed a prostatic STUMP with moderate cellularity and marked pleomorphism, lack of mitotic figures, necrosis, and stromal overgrowth. The tumor involved the left lobe within the capsule, and the resection margin was clear. By immunohistochemistry, the atypical stromal cells displayed strong and diffuse immunoreactivity for CD34 and PR, focal immunoreactivity for SMA, and no significance all the other markers detected. At the 41-month postoperative follow-up, there was no evidence of tumor recurrence or metastasis. The second patient was a 60-year-old man who complained of dysuria and bladder outlet obstruction. PSA was 1.9 ng/ml. TURS revealed an increased prostate volume and cystoscopy demonstrated enlarged prostate adenoma which was subsequently resected. Histologic examination showed a prostatic stromal tumor with phyllodes tumor-like growth patterns. Immunostaining for PR and CD34 and negative for SMA, desmin, CD117, DOG-1 of the atypical stromal cells confirmed the diagnosis of phyllodes tumor of the prostate (STUMP). This patient denied radical surgery and he was in a good status without tumor recurrence after 39 months.