(P 200) EPIDEMIOLOGY OF TENOSYNOVIAL GIANT CELL TUMOR IN THE UNITED STATES

Objective: Tenosynovial giant cell tumor (TGCT) is a rare non-malignant neoplasm involving the synovium and tendon sheaths that typically presents in young and middle-aged adults.1 TGCT is usually a monoarticular disease that involves the bone, soft tissue, synovium, or tendon sheath of small or large joints. Initial symptoms are often minimal due to the slow progressive nature of the disease, but as the tumor mass grows within the intra articular space and surrounding tissue, symptoms can progress from mild to debilitating. Commonly reported symptoms include pain, stiffness, swelling, and reduced range of motion of the affected joint, which can become severe and result in marked functional limitation.2

Localized TGCT (L-TGCT) is usually a benign neoplasm, most commonly occurring in the digits.3 Diffuse TGCT (D-TGCT) is a locally aggressive, nonmalignant neoplasm composed of synovial-like mononuclear cells, multinucleate giant cells, foam cells, siderophages, and inflammatory cells which may be intra-articular or extra-articular. D-TGCT most commonly occurs in large joints, particularly the knee as well as the ankle and hip.4

There is paucity of published scientific literature on the epidemiology of TGCT. Only two population-based studies, one from the Netherlands (Mastboom et al., 2017) and the other from Denmark (Ehrenstein et al., 2017) have reported TGCT incidence rate estimates.1,3 Moreover, the single study (Myers and Masi, 1980), estimating the incidence of TGCT in the US is based on one US-county.5 No studies have been conducted that provide the population-based estimates of TGCT incidence and prevalence in the United States (US). The goal of this research is to estimate the overall and gender-specific annual incidence and prevalence of L-TGCT and D-TGCT in the US.

Methods: To estimate the burden of both L-TGCT and D-TGCT in the US, overall and gender-specific TGCT incidence rates reported by Mastboom et al. (2017) in the Netherlands1 were extrapolated to the age- and gender-specific US population based on 20206 census estimates. Overall and gender-specific prevalence reported by Ehrenstein et al. (2017) in Denmark3 were extrapolated to the overall and gender-specific adult (≥18 years) US population census estimates for 20206 to calculate the prevalence of TGCT in the US.

Results: The estimated overall annual incidence of L-TGCT of digits was 11,059 (Females=6,632 and Males=4,305), 3,578 new cases of L-TGCT of extremities (Females=2,155 and Males=1,435), and 1,626 new cases of D-TGCT (Females=995 and Males=638). This corresponds to an overall annual incidence 16,263 of TGCT in the US in 2020 (Localized=14,637; Diffuse=1,626).
The estimated adult prevalence of L-TGCT was 144,094 (Females=88,044 and Males=56,290) and D-TGCT is 37,405 of (Females=20,063 and Males=17,541). This yields an overall estimated prevalence of 181,499 of adult TGCT in the US in 2020.

Conclusion: These results suggest that in the United States, the estimated prevalence of L-TGCT and D-TGCT are 144,094 and 37,405 respectively. Thus, there exists an estimated prevalence of 181,499 adult TGCT patients in the US. These estimates reveal that a large population of TGCT patients exists in the United States with a significant unmet need. Surgery, repeat surgery due to recurrence, and pexidartinib are the only treatment options available for these patients. In the United States, pexidartinib is the only drug approved by the Food and Drug Administration for the treatment of adult patients with symptomatic TGCT associated with severe morbidity or functional limitations and not amenable to improvement with surgery. Future efforts are needed to identify and develop additional treatment options for this underserved patient population.