Solitary fibrous tumour: histological discoveries, behavioural aspects, risk assessment and therapeutical approaches

Solitary fibrous tumours (SFT) are fibroblastic mesenchymal tumours that can develop virtually at any site. It usually affects adults, and its incidence is estimated as 1 new case per million people per year. SFT is characterized by a gene fusion involving NAB2 (NGFI-A-binding protein 2) and STAT6 (signal transducer and activator of transcription 6); a higher nuclear STAT6 immunostaining can be seen in SFT cells, and it is considered an excellent marker for immunohistochemical diagnosis. The 2020 WHO classification defines two categories for SFT: intermediate (rarely metastasizing) and malignant. Many risk stratification models have been proposed to predict the behaviour of these tumour identities. In case of localized SFTs, the cornerstone of the treatment remains surgery with the aim of negative margins (R0) when technically feasible. In intermediate/high-risk SFTs with positive margins (R1/R2) with no possibility to re-resection or in meningeal high-risk SFTs, adjuvant radiotherapy (RT) could be performed. Neoadjuvant RT could also have a role in both extra-meningeal and meningeal localizations. Sole RT could have a role in managing non-resectable SFTs even in a curative intent. Medical therapy plays an important role in the metastatic/advanced SFTs. Conventional chemotherapy may be used, with doxorubicin and dacarbazine being active though yielding poor responses. Other active drugs with currently ongoing studies in SFT are eribulin and trabectedin. Antiangiogenetic treatments have also been shown to provide benefit in this histological subtype. An area of recent investigation is immunotherapy, with an ongoing randomized trial comparing nivolumab + ipilimumab versus pazopanib in advanced rare soft tissue sarcomas, including SFTs. Despite its rarity and therefore the difficulty in performing prospective randomized trials with a large number of patients, many promising results in perioperative (radiotherapy) or in the metastatic (medical therapy) setting have been obtained. This review overviews the main characteristics and provides the current knowledge on standard therapies.