Background: Eighteen percent of breast cancer survivors will develop a second cancer within 25 years of diagnosis, of which breast cancer is the most common type. We have previously reported a higher cancer mortality among survivors who had a second cancer compared to a first cancer. In this study, we examined whether the increased cancer mortality from a second breast cancer differs by race/ethnicity. Method: A prospective cohort study was conducted among breast cancer survivors who developed a second breast cancer using data collected from the Surveillance, Epidemiology, and End Results (SEER) 18 database between 2000 and 2016. Hazard ratio (HR) and 95% confidence interval (CI) for cancer mortality after second breast cancer were estimated from Cox proportional hazard regression, comparing Non-Hispanic Black (NHB), Non-Hispanic American Indian/Alaska Native (NHAIAN), Non-Hispanic Asian/Pacific Islander (NHAPI), and Hispanic women to Non-Hispanic White (NHW) women. Models were adjusted for age at diagnosis, year of diagnosis, tumor stage, tumor grade, estrogen receptor (ER) status, and treatments (surgery, radiotherapy, and chemotherapy) of the second breast cancer. Analyses were also stratified by second cancer ER status, tumor stage, age at diagnosis (<50, 50-75, and ≥75 years), and time since first breast cancer diagnosis (≤5 and >5 years). In a subgroup of women diagnosed of second cancer after 2010 (N=8,224), we also conducted the analysis stratified by breast cancer molecular subtype [luminal A, triple-negative, and human epidermal growth factor receptor 2 (HER2)-positive]. Results: There were 14,392 breast cancer survivors diagnosed with a second breast cancer, including 9,928 NHW, 1,975 NHB, 70 NHAIAN, 988 NHAPI, and 1,431 Hispanic during the study period. The median age at diagnosis of the second cancer ranged from 57 to 66 years and the median follow-up time from diagnosis to cancer death ranged from 52 to 62 months across racial and ethnic groups. Cancer mortality was increased among NHB (HR: 1.28, 95%CI: 1.15-1.43) and Hispanic survivors (HR: 1.17, 95%CI: 1.03-1.33) compared to NHW. There was no increased cancer mortality among NHAIAN (HR: 1.07, 95%CI: 0.61-1.90) and NHAPI survivors (HR: 0.94, 95%CI: 0.80-1.12). The increased cancer mortality in NHB was observed irrespective of second cancer ER status, tumor stage, age at diagnosis, and time since first breast cancer diagnosis. Increased cancer mortality in NHB was also observed for luminal A (HR: 1.26, 95%CI: 1.11-1.44) and triple-negative subtypes (HR: 1.42, 95%CI: 1.10-1.83), but not for HER2-positive (HR: 1.19, 95%CI: 0.88-1.60) disease. For Hispanic patients, increased cancer mortality was observed in women with ER-positive disease, regional stage disease, cancer diagnosed <50 years of age, and cancer developed after 5 years. Conclusion: Racial/ethnic disparities in cancer mortality are present even among NHB and Hispanic breast cancer survivors who developed a second breast cancer. Studies are needed to understand the drivers of these disparities and to test preventive strategies to mitigate them.

Citation Format: Zhengyi Deng, Miranda R Jones, Mei-Cheng Wang, Kala Visvanathan. Racial/ethnic disparities in cancer mortality after a second breast cancer [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-14-05.