Abstract
Meningeal solitary fibrous tumor (SFT)/hemangiopericytoma (HPC) is a rare tumor with propensity for recurrence and metastasis. Although multiple classification schemes have been proposed, optimal risk stratification remains unclear, and the prognostic impact of fusion status is uncertain. We compared the 2016 WHO CNS tumor grading scheme (CNS-G), a three-tier system based on histopathologic phenotype and mitotic count, to the 2013 WHO soft-tissue counterpart (ST-G), a two-tier system based on mitotic count alone, in a cohort of 133 patients [59 female, 74 male; mean age 54 years (range 20–87)] with meningeal SFT/HPC. Tumors were pathologically confirmed through review of the first tumor resection (n = 97), local recurrence (n = 35), or distant metastasis (n = 1). A STAT6 immunostain showed nuclear expression in 132 cases. NAB2–STAT6 fusion was detected in 99 of 111 successfully tested tumors (89%) including the single STAT6 immunonegative tumor. Tumors were classified by CNS-G as grade 1 (n = 43), 2 (n = 41), or 3 (n = 49), and by ST-G as SFT (n = 84) or malignant SFT (n = 49). Necrosis was present in 16 cases (12%). On follow-up, 42 patients had at least one subsequent recurrence or metastasis (7 metastasis only, 33 recurrence only, 2 patients had both). Twenty-nine patients died. On univariate analysis, necrosis (p = 0.002), CNS-G (p = 0.01), and ST-G (p = 0.004) were associated with recurrence-free (RFS) but not overall survival (OS). NAB2–STAT6 fusion type was not significantly associated with RFS or OS, but was associated with phenotype. A modified ST-G incorporating necrosis showed higher correlation with RFS (p = 0.0006) and remained significant (p = 0.02) when considering only the primary tumors. From our data, mitotic rate and necrosis appear to stratify this family of tumors most accurately and could be incorporated in a future grading scheme.
Highlights
Meningeal solitary fibrous tumor (SFT)/hemangiopericytoma (HPC) is an often aggressive mesenchymal tumor of fibroblastic origin that arises from the cranial or spinal dura [14]
While the NAB2–STAT6 fusion seems to be unique to SFT/HPC, its detection may be difficult unless whole-genome sequencing is applied to detect breakpoints that occur both in exon and intron boundaries [5, 16]
The current 2016 WHO central nervous system (CNS) grading scheme incorporates phenotype and mitotic rate to stratify tumors into three groups, while non-meningeal soft-tissue tumors are classified by mitotic rate alone into SFT and malignant SFT according to the 2013 WHO classification for soft-tissue tumors [10, 14]
Summary
Meningeal solitary fibrous tumor (SFT)/hemangiopericytoma (HPC) is an often aggressive mesenchymal tumor of fibroblastic origin that arises from the cranial or spinal dura [14]. Tumors arising from the meninges tend to exhibit high rates of local recurrence with propensity for metastasis outside the central nervous system (CNS), but prognostication on histopathology alone has been notoriously difficult regardless of site of origin. Our earlier work suggested that tumors harboring the NAB2 exon 4–STAT6 exon 3 fusion variant exhibited morphologic features similar to the conventional solitary fibrous tumor, while there was a trend toward an association with the hemangiopericytoma phenotype and more aggressive behavior in tumors lacking this variant [11]. We studied a large series of patients with SFT/HPC from six tertiary care centers, to determine the best grading scheme for meningeal-based SFT/HPT and characterize the relationship of NAB2–STAT6 fusion status with phenotype and prognosis
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