Incidence of extrameningeal solitary fibrous tumors

Abstract

We commend Haas et al1 on their expansive retrospective analysis of treatment-related outcomes for extrameningeal solitary fibrous tumors (SFTs). After accounting for confounding factors, they have concluded that perioperative radiotherapy is associated with improved local control but not overall survival. This study represents the largest series to examine local failure rates for extrameningeal SFTs after radiotherapy to date and, in our opinion, is the most impactful. The authors emphasize the importance of their study and state that prospective, randomized studies are unlikely because of the rarity of the tumor. To support this assertion, they reference our study, which estimated 230 cases diagnosed in the United States per year.2 This statistic is used out of context because it refers to meningeal, not extrameningeal, SFTs/hemangiopericytomas (HPCs). Even though an incidence of 0.2 per 100,000 persons per year is frequently cited for extrameningeal SFTs, we found no primary literature from which this statistic is derived. We, therefore, queried the Surveillance, Epidemiology, and End Results database to determine the incidence of extrameningeal SFTs and HPCs (now collectively classified as SFTs) in the United States from 2000 to 2016.3, 4 The age-adjusted incidence rate was 6.1 (95% confidence interval [CI], 5.7-6.5) per 10,000,000 persons per year. In males and females, the age-adjusted incidence rates were 6.4 (95% CI, 5.8-7.0) and 5.9 (95% CI, 5.4-6.5), respectively. In contrast to meningeal SFTs/HPCs, there was no significant difference in age-adjusted incidence by race (6.2 [95% CI, 5.8-6.7] for whites, 5.6 [95% CI, 4.4-6.9] for blacks, 4.1 [95% CI, 1.5-8.8] for American Indians/Native Hawaiians, and 5.1 [95% CI, 3.9-6.4] for Asians or Pacific Islanders, Table 1), and there was no significant change in age-adjusted incidence over time. Thus, the epidemiology of extrameningeal SFTs appears to be distinct from that of SFTs of meningeal origin. On the basis of the crude incidence rate, which was also stable over time, we estimate 207 cases diagnosed in the United States in 2019. We agree with the authors that a prospective, randomized trial is unlikely. The significance of the authors' findings and conclusions regarding treatment recommendations remains unchanged. No specific funding was disclosed. Tony J. C. Wang reports personal fees and nonfinancial support from AbbVie, Elekta, Merck, Novocure, and the RTOG Foundation and personal fees from AstraZeneca, Cancer Panels, Doximity, Rutgers, the University of Iowa, and Wolters Kluwer outside the submitted work. The other author made no disclosures.

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