Solitary Fibrous Tumors: Clinicopathologic Spectrum and Risk Stratification From Tertiary Care Centers in India

Solitary fibrous tumor (SFT) is an uncommon fibroblastic mesenchymal neoplasm that may arise at virtually any anatomical site, but is more common in the pleural location.SFTs are characterized by a prominent, branching, thin-walled, dilated (staghorn) vasculature and NAB2-STAT6 gene rearrangement.Although most SFTs pursue an indolent clinical course, a subset demonstrates aggressive behavior with local recurrence, distant metastasis, or malignant transformation.The primary aim of the study was to study the clinicopathological profile and risk stratification profile of SFT with attention to atypical sites.The secondary aim was to study the Immunohistochemical profile and malignant transformation frequency in a series of SFTs in a defined population.This is a retrospective study that included 20 cases of SFT diagnosed over a defined period of time.Of these 20 cases, six (30%) are pleural and 14 (70%) are extra-pleural.Of the extra-pleural locations, some rare locations were noted in the temporal lobe and para-testicular region.Histologically, most tumors demonstrated the characteristic patternless architecture with alternating hypercellular and hypocellular areas, branching ("staghorn") vasculature, and variable collagen deposition.Immunohistochemistry was performed and all the cases showed strong positivity for vimentin, CD34 and STAT6.Malignant transformation was seen in two cases to fibrosarcoma and one case showed dedifferentiation to angiosarcoma.We also did risk assessment of the cases and found that out of 20 cases there were 17 cases in the low-risk category, two cases in the intermediate category and one case in the high-risk category.Long-term followup was not available.To conclude, SFT exhibits a broad morphological spectrum with variable biological behavior.Comprehensive histopathological evaluation combined with STAT6 immunohistochemistry and the Demicco risk assessment model provides a useful framework for prognostic stratification.