Abstract C062: Racial and ethnic disparities in risk of second primary non-breast cancer in breast cancer survivors
Authors: Mukherjee Amrita , Gu Zheng , Chen Lie H. , Haque Reina 
Published: September 2024

Abstract
Purpose: Disparities in cancer outcomes are multifactorial and are attributed to differences in access to care, socioeconomic status, tumor characteristics, treatment, family history, and comorbidity burden. Studies evaluating disparities in breast cancer outcomes have mostly been restricted to Black and White patients. Additionally, whether racial and ethnic disparities affect the risk of second primary cancer in breast cancer survivors, remains under-studied. We evaluated disparities in risk of second primary non-breast cancer in a racially and ethnically diverse cohort of breast cancer survivors treated at an integrated healthcare system. Methods: This retrospective cohort study included 37,222 breast cancer patients (aged ≥18 years) diagnosed between 2008-2020 at Kaiser Permanente Southern California (KPSC). Data on tumor characteristics, cancer treatments and sociodemographic variables were extracted from KPSC’s cancer registry and electronic health records. Patients were followed electronically from breast cancer diagnosis until they developed second primary non-breast cancer, died, disenrolled from the health plan, or reached study’s end (12/31/2021), whichever occurred first. Cox proportional hazards regression was used to report the association [Hazard Ratio (95% Confidence Interval)] between race and ethnicity and second primary non-breast cancer. Results: More than half of the study cohort consisted of non-Hispanic White survivors (51.2%), followed by 20.9% Hispanic survivors, 13.9% Asian/Pacific Islander (API) survivors, 12.7% non-Hispanic Black survivors, and 1.3% survivors of other/mixed races. Overall, 55.7% and 23.9% were diagnosed with local and regional breast cancer, respectively. During a median follow-up of 5.2 years, 4.6% survivors developed second primary non-breast cancers. In the multivariable model adjusted for sociodemographic characteristics, breast tumor characteristics, and breast cancer treatments, Hispanic and API survivors were 25% and 28% less likely to develop second primary cancer compared to White survivors [adjusted HR (95%CI): 0.75 (0.65-0.86)] and 0.72 (0.61-0.86), respectively]. We did not find an increased risk in Black survivors compared to White survivors [adjusted HR (95%CI): 0.91 (0.78-1.04)]. However, factors related to higher risk of second primary non-breast cancers were older age at breast cancer diagnosis, smoking, and higher comorbidity burden. Conclusion: Interestingly, risk of second primary non-breast cancer was lower in Hispanic and API survivors compared to White survivors in this insured cohort. Next steps will include examining which lifestyle factors (e.g. less smoking), or if pharmacological management of modifiable comorbidities might have played a role in the decreased risks seen in these two racial and ethnic groups.
Citation Format: Amrita Mukherjee, Zheng Gu, Lie H. Chen, Reina Haque. Racial and ethnic disparities in risk of second primary non-breast cancer in breast cancer survivors [abstract]. In: Proceedings of the 17th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2024 Sep 21-24; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2024;33(9 Suppl):Abstract nr C062.