[Evolution of grading for solitary fibrous tumors of the central nervous system: a clinical pathological and prognostic analysis].

Objective: The 5th edition of the WHO classification of central nervous system (CNS) tumors in 2021 made significant revisions to the nomenclature and grading system of solitary fibrous tumors (SFT). This study aimed to explore the changes in the grading of CNS SFT and its relationship with clinical pathological features and prognosis. Methods: This study retrospectively reviewed the clinical and pathological data of 82 patients with CNS SFT diagnosed at the First Affiliated Hospital of Fujian Medical University from March 2006 to June 2021, reassessed their grading according to the WHO 5th edition CNS tumor classification, and conducted a comprehensive analysis of their histological morphology, immunohistochemical characteristics, and clinical imaging data. Results: The age of the patients ranged from 21 to 83 years, with a median age of 48 years. Follow-up was completed for 82 patients, during which 10 patients died, 24 recurred, and 5 metastasized. MRI imaging showed that SFT exhibited isointense signals on T1-weighted imaging (T1WI) and complex signals on T2-weighted imaging (T2WI), with signal intensity decreasing as the content of collagen fibers increased. According to the 2021 grading criteria, there was a significant change in the grading of SFT, with the number of grade 1 SFT increasing from 10 cases under the 2016 standard to 39 cases, while the number of grade 2 and 3 SFT decreased accordingly. The 2016 grading system was significantly correlated with the overall survival (OS) of patients (P=0.009), while the 2021 grading system did not reach statistical significance. Both grading systems were correlated with histological phenotype, Ki-67 index, mitotic figures, and necrosis (P＜0.05). All cases expressed STAT6, and showed varying degrees of expression of vimentin, CD99, BCL-2, and CD34. The staining intensity of type Ⅳ collagen fibers, as analyzed semi-quantitatively, was correlated with the OS of the patients (P=0.017). Conclusions: The new grading system for CNS SFT has undergone significant changes, and its association with OS requires further validation. In-depth study of the content and fine structure of collagen fibers in SFT may have important clinical significance for the prognosis assessment and the formulation of treatment plans for patients. Moreover, quantitative analysis of T2WI signal intensity may provide a new method for preoperative preliminary assessment of the collagen fiber content in SFT.