Solitary fibrous tumour: A case series of a deceptively simple neoplasm in a tertiary care centre in South India

Background: Solitary fibrous tumours (SFTs) are uncommon mesenchymal neoplasms that show fibroblastic differentiation with a characteristic NAB2-STAT6 gene fusion. These tumours can occur at various sites and often follow an indolent course with infrequent metastases. Clinical and histological features predict aggressive behaviour. Our aim was to study the clinicopathological behaviour of these rare tumours, apply a risk stratification model to assess the risk of recurrence and highlight their different avatars. Methods: Cases diagnosed as SFT with immunohistochemical (IHC) confirmation in our department archives over the last 10 years were extracted. The morphological spectrum was analysed along with the correlation of available radiology and clinical data. The modified Demicco risk stratification model was applied on those cases with complete details to assess concordance with clinical behaviour. Results: A total of 23 cases of suspected SFT were studied; however, after exclusion of 5 cases due to lack of IHC confirmation, 18 patients (10 females and 8 males) were included in the study. The mean age was 55.8 years, with 10 patients above the age of 55 years. The most common site involved was the pleuropulmonary region (5 cases), accounting for 29% of the cases. The other sites of involvement included urinary bladder/ovarian hilum/pelvis (3 cases), extremities (2 cases), abdominal/peritoneal (2 cases) and one case each in the dura, ethmoid sinus, parotid gland, breast, vertebra and conjunctiva. The mean follow-up period was approximately 29 months; five cases showed local recurrence in this period and belonged to the moderate risk category and one case was metastatic SFT in the vertebra. Conclusions: Although rare, SFT should be considered in the differential diagnosis of spindle cell lesions even in unusual locations, and appropriate immunohistochemistry is mandatory. Once the diagnosis is established, documentation of histological features such as mitotic rate and necrosis, along with tumour size, is essential for risk stratification/prognostication. Dedifferentiated SFT is a tumour to be kept in mind when faced with a ‘difficult to classify’ high-grade neoplasm at any site.