Abstract 1182: Racial and ethnic disparities in incidence of Langerhans Cell Histiocytosis differ across age groups
Authors: Peckham-Gregory Erin Christine , McClain Kenneth , Allen Carl , Lupo Philip , Scheurer Michael 
Published: September 2020

Abstract
Introduction: Langerhans cell histiocytosis (LCH) is a myeloid neoplasia with median diagnosis age of 30 months. We recently reported an increased risk for LCH in children of Hispanic parents using data from the Texas Cancer Registry. However, less is known about racial/ethnic disparities among adults diagnosed with LCH. Therefore, we sought to compare the incidence of LCH by race/ethnicity in the United States among pediatric, adolescent/young adult (AYA), and adult cases using Surveillance, Epidemiology, and End Results (SEER-18) program data.
Methods: LCH incidence data were obtained from the SEER-18 program, 2000-2016. Race/ethnicity was categorized as: non-Hispanic white (NHW); non-Hispanic black (NHB); non-Hispanic Asian (NHA); and Hispanic. Age-specific incidence rate ratios (IRRs) and 95% confidence intervals (CIs) were generated in SEER-STAT (v8.3.6).
Results: Data on cases with LCH ages 0-14 (nchildren=894), 15-39 (nAYAs=246), and 40+ (nadults=341) were abstracted. Compared to NHW children, Hispanic children experienced significantly elevated IRRs (IRRHispanic_children=1.28, 95% CI: 1.10-1.48). However, this trend was not observed among AYAs (IRRHispanic_AYAs=0.57, 95% CI: 0.40-0.80) or adults (IRRHispanic_adults=0.47, 95% CI: 0.29-0.73) where lower IRRs compared to NHWs were evident. While not statistically significant across all age groups, this trend was also suggested among NHAs. Compared to NHW children, IRRs for NHAs were slightly elevated (IRRNHA_children=1.19; 95% CI: 0.93-1.51), whereas among AYAs a trend toward lower incidence was evident (IRRNHA_AYAs=0.57, 95% CI: 0.32-0.94) and became stronger among NHA adults (IRRNHA_adults=0.52, 95% CI: 0.31-0.84). NHBs experienced lower IRRs compared to NHWs in all age groups that reached a level of statistical significance: (IRRNHB_children=0.43, 95% CI: 0.31-0.57; IRRNHB_AYAs=0.48, 95% CI: 0.28-0.77; and IRRNHB_adults=0.50, 95% CI: 0.30-0.79). These estimates remained similar after adjusting for sex and SEER registry using Poisson regression.
Conclusion: This study demonstrates that the incidence of LCH by racial/ethnic group varies substantially across the age spectrum. Specifically, Hispanic pediatric LCH cases experience a unique increase in incidence compared to NHWs that is not observed among Hispanic AYAs or adults, or among other racial/ethnic groups. These results align with previous studies that indicate Hispanic children in the lowest age groups experience the highest risk of LCH compared to NHWs. Additionally, NHBs in all age groups experienced a decreased incidence of LCH compared to NHWs; an observation historically noted in the literature. Overall, these contrasts in incidence by race/ethnicity may suggest differences in underlying LCH etiology across the age spectrum, and particularly in children. While limitations of registry data exist, future studies characterizing molecular components in adults compared to children is warranted.
Citation Format: Erin Christine Peckham-Gregory, Kenneth McClain, Carl Allen, Philip Lupo, Michael Scheurer. Racial and ethnic disparities in incidence of Langerhans Cell Histiocytosis differ across age groups [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1182.