A retrospective multicenter study of WHO 2021 classification-diagnosed solitary fibrous tumor of the CNS in a population from Lombardy, Italy

In this retrospective, multicenter study, we collected patients with solitary fibrous tumor-SFT-of the CNS followed in eight hospitals in Lombardia from 2004 to 2019, revising the diagnosis according to the WHO 2021 classification. Clinical data were analyzed at diagnosis and during follow-up. Overall, 57 patients were enrolled, of whom 52.6% female. Median age was 54, 91% had an intracranial tumor and 9% a spinal location. 49% patients had grade 1, 31.5% grade 2 and 19% grade 3 tumor. After a median follow-up of 84 months, 49% of the patients had progressed and 8.7% had died. Gross tumor resection was obtained in 70%, subtotal in 26.3%, partial in 1.7% and biopsy in 1.7%. 15.7% (n = 9) of patients developed extra-CNS metastases, mainly involving bone, lung and liver, six of these were grade 3 and 3 were grade 2 at first diagnosis. 14 patients (24.5%) underwent radiation therapy, 3 chemotherapy and one received liver transplant. The 14 radiation-treated patients included all grade 3 and 3 grade 2 with partial or subtotal resection. Only tumor grade had a prognostically significant impact on PFS at univariate analysis, while age had not. All but one case displayed nuclear expression for STAT6, the remaining case showed diffuse expression of CD34. Whereas grade 3 was confirmed as a prognostically relevant factor, partially overlapping behaviours were detected in patients usually considered at low (all grade 1 and grade 2 with gross total resection) versus moderate risk (grade 2 with biopsy or non-gross total resection).