[P-18] Solitary fibrous tumour of the prostate: a rare mesenchymal neoplasm – a case report

Prattana Chiravirakul

Anatomical Pathology Department, Lampang Hospital, Lampang, Thailand

Background: Solitary fibrous tumour (SFT) is an uncommon myofibroblastic tumour generally affecting the pleura. Differential diagnosis includes poorly differentiated adenocarcinoma and various mesenchymal neoplasm of prostate.

Case Presentation: A 66-year-old man presented with dysuria for 8 months. He was diagnosed as benign prostatic hyperplasia and he received medical treatment but his symptoms did not improve. The transurethral resection of prostate (TUR-P) was performed. The macroscopic examination showed multiple irregular firm light brown tissue, measuring 4 x 3 x 1 cm in aggregate and weighing 30 grams. The microscopic sections showed patternless spindle cell proliferation, embedded in fibrous stroma. Multiple staghorn blood vessels were identified in the lesion. Some areas showed hypercellularity and pleomorphic nuclei. Few areas of necrosis were noted. Mitotic rate was 1 – 2/10 HPFs. So careful long-term clinical follow-up was recommended. Immunostainings showed positivity for vimentin, CD34, PR and desmin while it was immunonegative for CD117, SMA, PSA and uroplakinII. The further immunostaining for STAT6 was performed and showed strong positivity. The solitary fibrous tumour was finally diagnosed in this case.

Discussion and Conclusion: SFT is rare prostatic mesenchymal neoplasm. The immunohistochemical study should be performed in panel approach. The STAT6 immunostaining is specific for SFT. The malignant features of SFT are high cellularity with cytological atypia, necrosis and increased mitotic activity (> 4/10 HPFs) or atypical mitosis.