A Comprehensive Review on Solitary Fibrous Tumor: New Insights for New Horizons

Abstract

Solitary fibrous tumor (SFT) is a rare mesenchymal, ubiquitous tumor, with an incidence of 1 new case/million people/year. In the 2020 WHO classification, risk stratification models were recommended as a better tool to determine prognosis in SFT, to the detriment of “typical” or “malignant” classic terms. The risk for metastasis is up to 35–45%, or even greater, in series with a longer follow-up. Over the last few decades, advances in immunohistochemistry and molecular diagnostics identified STAT6 nuclear protein expression and the NAB2–STAT6 fusion gene as more precise tools for SFT diagnosis. Recent evidence taken from retrospective series and from two prospective phase II clinical trials showed that antiangiogenics are active and their sequential use from first line should be considered, except for dedifferentiated SFT for which chemotherapy is the best option. Since the fusion transcript driver’s first description in 2013, new insights have been brought on key molecular events in SFT. This comprehensive review mainly focuses on the superior efficacy of antiangiogenics over chemotherapeutic agents in SFT, provides the current knowledge of key molecules that could co-drive the SFT behavior, and suggests new target candidates that deserve to be explored in preclinical and clinical research in SFT.

A Case Report of a Solitary Fibrous Tumor of the Maxillary Sinus

“…While these features are consistent with those previously reported in literature, it has to be said that none of them are pathognomonic of SFT [3]. Therefore, the differential diagnosis must include glomangiopericytoma, inverted papilloma, hemangioma, leiomyomas, schwannoma, squamous cell carcinoma, juvenile angiofibroma, angiomatous polyps, nerve sheets tumors, mesenchymal chondrosarcoma, and byphenotipic synovial sarcoma [7][8][9]. The former definition of hemangiopericytoma has been integrated under the SFT nomenclature in the 2013 WHO classification [6].…”

Solitary Fibrous Tumor: Integration of Clinical, Morphologic, Immunohistochemical and Molecular Findings in Risk Stratification and Classification May Better Predict Patient outcome

“…Detection of the specific fusion gene NAB2/STAT6 and its variants confirm a diagnosis of SFT, especially in rare clinical settings, unusual histological findings or unexpected immunohistochemical results. Moreover, specific gene fusions have been related to prognosis and tumor location [7,8,11,12,[26][27][28][29][30][31][32][35][36][37][38][39][40][41][42]. Various risk-stratification systems (RSS) have been described, with the Demicco et al system being the most widely implemented, as recommended in the World Health Organization (WHO) blue book [1][2][3][4][5]14].…”

“…However, some of these cases may have late recurrence/relapse and/or metastases leading to uncertainty and skepticism among oncologists regarding the specificity of RSS in correctly predicting evolution in all cases [1][2][3][4][5]14]. Furthermore, molecular results have not been included in any of the present RSS so far [1][2][3][4][5][6][7][8]42].…”

“…The evolution of SFTs is often uncertain [2][3][4][5][6][7][8][9][10]. Although most cases evolve favorably, a small group can progress towards dissemination, generally pulmonary, as well as other locations, and will lead to patient death in the absence of effective treatments [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19]. Thus, valid and reproducible tools should be developed in order to design risk-tailored treatment and risk-adjusted follow-up.…”

“…Aberrant epithelial, muscular or neuroendocrine marker expression has been described which may lead to confusion with other tumors that share a similar morphology [15][16][17][18][19][20][21][22][23][24][25]36]. The fusion gene NAB2/STAT6 and its variants confirm a diagnosis of SFT in those cases with unconvincing STAT6 immunoreactivity, and specific gene fusions have been related to prognosis and tumor location [6][7][8][9][10][11][12][13][14][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40]. STAT6 nuclear expression is not exclusive to SFTs and has also been reported in dedifferentiated liposarcoma, glioma-associated oncogene homolog 1 (GLI1)-amplified tumor, Kaposi sarcoma and Hodgkin as well non-Hodgkin lymphomas [6,[12][13][14][15][16][17][18][19][20]…”