A rare case of malignant solitary fibrous tumor in prostate with review of the literature

Abstract

BackgroundSolitary fibrous tumor is an uncommon soft tissue neoplasm with intermediate biological behavior, which rarely metastasizes. Malignant solitary fibrous tumor, although not clearly defined, is rarely described in the prostate. The present case is characterized by some peculiarities if compared with previously reported cases of prostatic malignant solitary fibrous tumor. Firstly, it does not show a homogeneous morphology: part of the neoplasm (about 50%) showed the features of a conventional solitary fibrous tumor, while the remaining part showed the features of a malignant solitary fibrous tumor. In addition, the case is the first malignant solitary fibrous tumor reaching a huge diameter of 20 cm and replacing all prostatic parenchyma. Interestingly, normal prostatic parenchyma was observed on left-lobe trans-rectal needle-core biopsies, but was totally absent in surgical specimen. Since radical prostatectomy was carried out about 4 months after the biopsies, such discordant data may suggest exceedingly rapid growth of the neoplasm.Case presentationWe report a case of a 62-year-old male, presented at medical observation for urinary retention, constipation and an enlarged prostate gland. A trans-rectal prostatic biopsy showed a low-grade spindle cell neoplasm. Histopathological examination of the prostatectomy specimen showed patternless architecture with hypocellular and hypercellular areas and hemangiopericytoma-like vessels. In some fields the neoplasm was characterized by a high mitotic index and evident cellular atypia. Immunohistochemically, neoplastic cells were positive for CD34, bcl2, CD99, STAT6 and partially for PgR. The neoplasm was diagnosed as a malignant solitary fibrous tumor.ConclusionsThe differential diagnosis of spindle cells tumors arising in the prostrate is broad and includes lesions of epithelial and mesenchymal origin, primary prostatic lesions such as stromal tumors of uncertain malignant potential and stromal sarcoma, as well as anatomically ubiquitous soft tissue neoplasms. Solitary fibrous tumors should be considered in cases of prostatic tumors with a spindled morphology, but malignancy in such tumors is extremely rare in the prostate. A review of literature showed only four additional cases. Because of the unpredictable biological behavior and the possibility of recurrence, a long-term clinical and instrumental follow-up is recommended.

Bladder Leiomyoma with Synchronous Solitary Fibrous Tumor of the Pleura

“…According to the World Health Organization, SFTs are classified as intermediate-rare metastatic tumors [5]. The main features of potential malignancy include tumor size (>15 cm), patient age (>55 years), and the presence of mitotic activity > 4/10 high fields of view (×400 magnification) [6]. None of these features was documented in our case, supporting a benign nature of the tumor.…”

“…Immunohistochemically, tumor cells expressed CD34, vimentin, and Bcl-2, showing no expression of smooth muscle actin (SMA), EMA, Cam 5.2, desmin, and calretinin. These findings were compatible with a SFT of the pleura [6]. At the time of diagnosis, imaging of the lower abdomen was not performed.…”

“…The histological examination revealed a benign neoplasm (3:3 × 2:7 × 2:2 cm) composed of dense intersecting fascicles of slender tapered smooth muscle cells, without mitotic activity, nuclear atypia, or areas of necrosis, arranged in a collagenous stroma containing vessels with mural hyalinization. Immunohistochemically, tumor cells expressed muscle antigens such as SMA and desmin, while they were negative for S-100 protein and CD34, [6]. Based on these findings, the diagnosis of BL was set.…”

“…Extrapleural SFTs are commonly located at the visceral skull and the retroperitoneum [5]. The presence of SFTs in the genitourinary system is extremely rare (14 cases of prostate SFTs [6] and <50 cases of renal SFTs [7] have been published). The pathogenesis of SFTs has not been elucidated, and they usually remain asymptomatic [5].…”

STAT6 monoclonal antibody is highly specific for the distinction between solitary fibrous tumour and prostatic stromal proliferations

“…Additionally, SFT and prostatic stromal neoplasms may also share expression for progesterone receptor, smooth muscle actin, CD99 and BCL2. 3,4 Multiple recent studies have reported the presence of a recurrent fusion gene involving NAB2 (a repressor of the transcription factors EGFR1 and EGFR2) and STAT6 (a transcription factor involved in the modulation of interleukin-4 and interleukin-13) in SFTs. 5 The occurrence of this intrachromosomal gene fusion is identified in the majority of SFTs, regardless of location.…”