Solitary 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.
We 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.
The 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.
Fletcher CDM, Bridge JA, Lee JC. Extrapleural solitary fibrous tumour. In: Fletcher CDM, editor. WHO classification of tumours ofsoft tissue and bone. 4th ed. Lyon: the International Agency for Research on Cancer press; 2013. p. 80–2.
Doyle LA, Vivero M, Fletcher CD, Mertens F, Hornick JL. Nuclear expression of STAT6 distinguishes solitary fibrous tumor from histologic mimics. Mod Pathol. 2014;27(3):390–5. PubMed
Cheville J, Algaba F, Epstein JI, Lopez-Beltran A. In: Moch H, editor. WHO classification of tumours of the urinary system and male genital organs. 4th ed. Lyon: the International Agency for Research on Cancer press; 2016. p. 177.
Hossain D, Meiers I, Qian J, Mac Lennan GT, Bostwick DG. Prostatic stromal hyperplasia with atypia: follow-up study of 18 cases. Arch Pathol Lab Med. 2008;132:1729–33. PubMed
Masuda Y, Kurisaki-Arakawa A, Hara K, et al. A case of dedifferentiated solitary fibrous tumor of the thoracic cavity. Int J Clin Exp Pathol. 2014;7:386–93. PubMed
Ouladan S, Trautmann M, Orouji E, et al. Differential diagnosis of solitary fibrous tumors: a study of 454 soft tissue tumors indicating the diagnostic value of nuclear STAT6 relocation and ALDH1expression combined with in situ proximity ligation assay. Int J Oncol. 2015;46(6):2595–605. PubMed
- A rare case of malignant solitary fibrous tumor in prostate with review of the literature
Elvira La Mantia
Marco De Sio
Annarosaria De Chiara
- BioMed Central