Solitary fibrous tumor of thoracic cavity, extra-thoracic sites and central nervous system: Clinicopathologic features and association with local recurrence and metastasis

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Abstract

Published risk stratification models of solitary fibrous tumor (SFT) have been associated with distant metastases outside the central nervous system (CNS), but have not been studied for tumors occurring in the CNS. In a retrospective review, we identified 72 cases of solitary fibrous tumor or hemangiopericytoma (HPC) diagnosed between January 2011 and December 2020 at our institution. The tumors involved the central nervous system (N = 17), thoracic cavity (N = 28), and extrathoracic sites (N = 27). The risk of local recurrence, distant metastasis, or death at 5 years was 57% (95% CI 23%, 76%) in the CNS, 24% (95% CI 2%, 41%) in the thoracic cavity, and 13% (95% CI 0%, 25%) in extrathoracic sites. By contrast, the risk of distant metastasis or death at 5 years was 13% (95% CI 0%, 29%) in CNS primaries, 5% (95% CI 0%, 14%) in thoracic primaries, and 14% (95% CI 0%, 27%) in extrathoracic primaries. Using the published 3- and 4-variable risk stratification models by Demicco et al., we retrospectively assessed our cases for risk of local recurrence, distant metastasis, and death. For tumors outside the CNS, we show that three- and four-variable risk stratification models were associated with recurrence-free survival in addition to the previously known association with distant metastasis (all P < 0.05). In contrast, inside the CNS, we show that neither risk model is a significantly associated with clinical behavior, and that WHO grade is likely the best available prognostic tool, though none of the differences were significant. The lack of significant differences can be likely explained by the younger median age (47 years vs 61 years) and smaller median tumor size (3.5 cm vs 5.6 cm), downgrading the risk stratification scores in CNS compared to non-CNS primaries. In conclusion, existing risk stratification models of SFT are not associated with clinical behavior for tumors arising inside the CNS, but are associated with local recurrence in addition to distant metastasis outside the CNS.

Introduction

Solitary fibrous tumor (SFT) is a mesenchymal neoplasm of fibroblastic type, encompassing a histological spectrum with two main morphological variants: the SFT phenotype characterized by a so-called patternless architecture or short fascicular pattern, with alternating hypocellular and hypercellular areas with thick bands of collagen, and the hemangiopericytoma (HPC) phenotype characterized by high cellularity and a delicate, rich network of reticulin fibers typically investing individual cells [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20], [21], [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44]. Thin-walled, branching vessels, called HPC-like or staghorn vessels, are a feature shared by both phenotypes. The discovery of a shared, recurrent NAB2-STAT6 gene arrangement in both SFT and HPC has confirmed the identical nature of these neoplasms [1], [2], [3], [17], [18], [19], [21], [32], [42]. SFTs may occur at any anatomical site, including pleural cavities, extremities, head and neck, abdominal cavity, pelvis, retroperitoneal space, visceral organs, bone, and central nervous system (CNS) [1], [2], [3]. Predicting the clinical behavior of SFT has long been a notoriously difficult task for both oncologists and pathologists [4]. The current 2016 WHO CNS grading scheme incorporates phenotype (SFT and HPC) and mitotic rate to stratify tumors into three groups (grade I, II, and III), while thoracic and extrathoracic tumors were classified by mitotic rate alone into SFT and malignant SFT according to the 2013 WHO classification for soft tissue tumors [1], [2], [5], [6], [7], [10], [14], [32]. However, it is well established that morphologically benign tumors may occasionally metastasize and conversely that many tumors, classified as malignant based on histologic findings, have an indolent clinical course [8], [9]. The development of risk models for the prediction of metastatic risk in SFTs has resulted in improved prognostication over the traditional benign/malignant dichotomy, and these models are recommended by the 2019 WHO classification of soft tissue tumors [1], [3], [4], [6], [10], [11], [12], [13], [14], [15], [45], [46], [47]. However, neither of these models have been validated for CNS SFT/HPC, nor have they been tested regarding their association with local recurrence in non-CNS sites. The aim of this study is to investigate the prognostic value of the published three- and four-variable risk stratification models by Demicco et al. [10], [11] for both local recurrence and distant metastasis in thoracic, extrathoracic, and CNS SFT in order to establish a unified risk assessment approach for these neoplasms.

Section snippets

Material and methods

The present study was approved by the Institutional Review Board of Northwestern Memorial Hospital.

Clinical characteristics

Data on anatomic location, age at presentation and gender are summarized in Table 1. SFTs occurred predominantly in females (54%, female to male ratio 1.2:1), with a median age of 56 years for females and 57 years for males. Tumors were located in the CNS (N = 17), thoracic cavity (N = 28), and extrathoracic sites (N = 27) (Fig. 1A). Patients with thoracic and extrathoracic SFT usually presented with a slowly enlarging mass of variable duration. In most cases of CNS tumors, the symptoms were

Discussion

To the best of our knowledge, our study is the first to test the performance of the published three- and four-variable risk stratification models by Demicco et al. [10], [11] for risk stratification of local recurrence in addition to distant metastasis, as well as to assess the performance of these models relative to WHO grading criteria for SFT/HPC in the CNS.

In this study, with regard to histologic appearances, CNS tumors were not perceptibly different from SFTs arising in the thoracic cavity

Conclusion

In this study, we show that for non-CNS tumors, both the three and four-variable risk stratification models by Demicco et al. [10], [11] and mitotic activity were significantly associated with metastasis-free and recurrence-free survival. By contrast, in CNS cases, no significant differences were seen in either metastasis-free or recurrence-free survival based on either the three- or four-variable risk models. Though none of the differences were significant, overall, WHO grade appears to be the

Funding

No external funds were obtained for this work.

CRediT authorship contribution statement

All co-authors have seen and agree with the contents of the manuscript and there is no financial interest to report. We certify that this manuscript is not under consideration elsewhere.

Conflict of interest

We declare that we have no conflict of interest.

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