Abstract 3724: Race/ethnicity, genetic ancestry, and breast cancer-related lymphedema
Authors: Kwan Marilyn L. , Lee Valerie S. , Roh Janise M. , Ergas Isaac J. , Zhang Yali , Kutner Susan E. , Quesenberry Charles P. , Ambrosone Christine B. , Kushi Lawrence H. , Yao Song 
Published: August 2015

Abstract
Background: Breast cancer-related lymphedema (BCRL) is a serious chronic condition that can occur in about 30% of patients after breast cancer (BC) surgery and treatment. Patient risk factors include younger age, higher BMI, and less physical activity. With few studies to date, it is largely unknown if BCRL risk varies by race/ethnicity.
Methods: In a prospective study of 2,953 BC patients, we examined the association of self-reported BCRL status at 12 and 48 months post-BC diagnosis with self-reported race/ethnicity and genetic ancestry. We also assessed associations with other clinical and patient factors. Race/ethnicity (White, African American (AA), Hispanic, Asian, and Other) was asked in the baseline interview at cohort entry. Genetic ancestry was estimated based on a validated panel of 124 ancestry informative markers (AIMs) using the STRUCTURE program. Hazard ratios (HR) and 95% confidence intervals (CI) were calculated by multivariable Cox proportional hazards models, with follow-up until date of BCRL self-report or last patient contact, whichever occurred first.
Results: 342 (11.6%) women reported having BCRL at 12 or 48 month follow-up, with 204 who were White, 37 AA, 41 Hispanic, 49 Asian, and 11 Other. Younger age at BC diagnosis, higher BMI at baseline, and less moderate-vigorous physical activity were associated with greater BCRL risk. After adjusting for sociodemographic and clinical factors, AA women had a significant 1.6-fold increased risk of BCRL (HR = 1.57; 95% CI: 1.09, 2.26) and Hispanic women had a borderline 1.4-fold increased risk (HR = 1.37; 95% CI: 0.99, 1.89), compared with White women. Consistent with self-reported race/ethnicity, African ancestry was associated with a 1.8-fold increased risk of BCRL (HR = 1.80; 95% CI: 1.15, 2.81). When the race/ethnicity and ancestry models were further adjusted for BCRL risk factors, i.e., age at BC diagnosis, BMI, and physical activity, associations became attenuated and non-significant among AA (HR = 1.26, 95% CI: 0.87-1.83) and Hispanic women (HR = 1.19, 95% CI: 0.85-1.68), and with African ancestry (HR = 1.38, 95% CI: 0.88-2.19). Results were similar when excluding BCRL events within 6 months of BC diagnosis to rule out transient post-operative swelling, except a suggestive increased risk of BCRL remained among AA women (HR = 1.47, 95% CI: 0.94-2.28) and with African ancestry (HR = 1.70, 95% CI: 0.99-2.91) after adjustment for BCRL risk factors. Further, the elevated BCRL risk seen in AA or Hispanic women, and with African ancestry, appeared to be stronger in non-obese compared with obese women.
Discussion: AA women had increased risk of BCRL compared with White women, which is partly attributed to differences in age at BC diagnosis, BMI, and physical activity. This is the first large-scale, prospective study to examine a racial/ethnic disparity of BCRL risk with self-report and genetic ancestry data.
Funded by R01 CA105274.
Citation Format: Marilyn L. Kwan, Valerie S. Lee, Janise M. Roh, Isaac J. Ergas, Yali Zhang, Susan E. Kutner, Charles P. Quesenberry, Christine B. Ambrosone, Lawrence H. Kushi, Song Yao. Race/ethnicity, genetic ancestry, and breast cancer-related lymphedema. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3724. doi:10.1158/1538-7445.AM2015-3724