Abstract 2297: Racial and ethnic disparities in incidence of Langerhans cell histiocytosis differ across age groups

Abstract Background: Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasia with a median diagnosis age of 30 months, though it can occur at any age. The estimated annual incidence is 5 cases per million children under the age of 15 and 1-2 cases per million adults. We previously reported an increased risk of LCH among children of Hispanic parents using data from the Texas Cancer Registry. However, less is known about differences in underlying biology between children and adults, and it is unclear whether incidence profiles differ across age groups. Therefore, this study aimed to compare the incidence of LCH by race/ethnicity in the United States (US) across the age spectrum using data from the US Cancer Statistics (USCS) database. Methods: LCH incidence data were obtained from the USCS database for the period 2001-2021, representing 99.6% of the US population, and stratified by age at diagnosis and race/ethnicity. Age was defined as childhood (0-14 years), AYA (15-39 years), and adult (40+ years). Race/ethnicity was categorized as non-Hispanic White (NHW), non-Hispanic Black (NHB), non-Hispanic American Indian or Alaska Native (NHAIAN), non-Hispanic Asian or Pacific Islander (NHAPI), and Hispanic. Age-adjusted incidence rate-ratios (IRRs) and 95% confidence intervals (CIs) were calculated using SEER*Stat (v8.4.4) to assess differences in LCH incidence across these groups. Results: We identified 3, 825 childhood, 1, 306 AYA, and 1, 718 adult LCH cases in the USCS database. Hispanic children showed significantly higher LCH IRRs (IRRHispanic_0-14=1.17, 95% CI: 1.09-1.26) compared to NHW children. However, this trend was not observed in Hispanic AYAs or adults, who exhibited significantly lower IRRs than NHWs. In a sub-analysis of childhood cases, Hispanic children aged 0-4 and 5-9 showed significantly higher LCH IRRs compared to NHW children (IRRHispanic_children_0-4=1.26, 95% CI: 1.14-1.39; IRRHispanic_children_5-9=1.16, 95% CI: 1.01-1.34), while this trend attenuated among Hispanics aged 10-14 (IRRHispanic_children_10-14=0.94, 95% CI: 0.79-1.12). NHBs showed significantly lower LCH IRRs across all age groups compared to NHWs as well as in sub-analyses of NHB children aged 0-4, 5-9, and 10-14 (IRRNHB_0-4=0.37, 95% CI: 0.31-0.45; IRRNHB_5-9=0.37, 95% CI: 0.27-0.48; IRRNHB_10-14=0.24, 95% CI: 0.16-0.35). Conclusions: This study reveals significant differences in LCH incidence by racial/ethnic group across ages. Hispanic pediatric cases show higher incidence compared to NHWs, particularly in children aged 9 and below, a trend not seen in Hispanic AYAs and adults. In contrast, NHBs exhibit a decreased incidence across all age groups compared to NHWs. These disparities in LCH incidence by race/ethnicity may suggest differences in underlying LCH etiology across the age spectrum. Future studies are warranted to characterize the molecular components of LCH in adults compared to children. Citation Format: Jessica Velazquez, Kenneth L. McClain, Philip J. Lupo, Carl E. Allen, Michael E. Scheurer, Erin C. Peckham-Gregory. Racial and ethnic disparities in incidence of Langerhans cell histiocytosis differ across age groups [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 2297.