Abstract IA27: Disparities in breast cancer survivorship and outcomes
Authors: Kushi Lawrence H. , Ergas Isaac J. , Roh Janise M. , Gomez Scarlett Lin , Kwan Marilyn L. , Thomsen Catherine , Yao Song , Ambrosone Christine B. 
Published: February 2019

In the U.S., women of European ancestry have historically had the highest incidence of breast cancer compared to other major race/ethnicity groups. In recent years, the incidence rate for black women has approached that of white women, while rates for Asian and Hispanic women are about 25% lower than for white or black women. However, once diagnosed with breast cancer, black women have poorer survival rates than white women. The most recent “Annual Report to the Nation on the Status of Cancer” using nationwide cancer-registry data from 2006-2013 (Jemal et al., JNCI, 2017) reported a higher age- and stage-adjusted relative mortality risk after breast cancer of 1.71 (95% confidence interval (CI), 1.66-1.76) for non-Hispanic blacks compared to non-Hispanic whites. Hispanic women also experienced a slightly increased relative mortality risk of 1.14 (95% CI, 1.10-1.18) compared to white women, while Asians experienced a lower relative mortality risk of 0.84 (95% CI, 0.80-0.88).

The reasons for such disparities in outcomes after breast cancer are complex. One suggested contributing factor is differences in access to care, as blacks and Hispanics tend to be of lower socioeconomic status than whites or Asians. It is possible to minimize the effects of access to health care by examining outcomes after breast cancer diagnosis in an integrated health care setting such as Kaiser Permanente Northern California (KPNC), in which all patients have health insurance coverage with access to the same health care providers. We are currently conducting the Pathways Study, a prospective cohort study of 4,505 women diagnosed with breast cancer with enrollment from 2006-2013. This diverse cohort includes 557 Hispanics, 578 Asians, and 358 blacks.

Preliminary analyses in the larger population of 11,176 women who were diagnosed with invasive breast cancer in KPNC and eligible for the Pathways Study found that, despite the uniform health care access, racial disparities in mortality after breast cancer were qualitatively similar to those observed nationally. With 1,738 total deaths as of September 20, 2016, and adjusted for age and stage at diagnosis, compared to white women, black women had an increased relative mortality risk of 1.59 (95% CI, 1.24-2.03). For Hispanic women, the relative risk was 0.92 (95% CI, 0.72-1.19), and for Asians it was 0.70 (95% CI, 0.51-0.97). Among the subset of women enrolled in the Pathways Study (n=538 total deaths), comparable relative risks were 1.74 (95% CI, 1.35-2.24) for black women, 0.99 (95% CI, 0.75-1.29) for Hispanic women, and 0.73 (95% CI, 0.52-1.02) for Asians. Similar black-white differences were also seen for breast cancer-specific mortality and recurrence in the Pathways Study cohort in which recurrences are being documented.

These observations indicate that health care access is unlikely to explain racial/ethnic disparities in breast cancer outcomes. As the Pathways Study, we will be able to explore aspects of health care utilization, such as treatment-related factors such as treatment delay, adherence, and early discontinuation. We will also be able to explore presence of comorbid conditions or use of non-cancer medications that may influence mortality and breast cancer outcomes. In the Pathways Study, we are collecting data on lifestyle and psychosocial factors (e.g., food intake, physical activity, social support, doctor-patient communications, and quality of life); linking to geospatial databases to characterize the social and built environment of cohort members; and conducting genome-wide assays. For example, in preliminary analyses that adjusted additionally for estrogen receptor status, body mass index, educational attainment, and physical activity, black-white differences in mortality persisted even though they were somewhat attenuated (relative risk of 1.43; 95% CI, 1.09-1.86).

Along with other studies that are examining breast cancer outcomes in different populations, the Pathways Study is poised to contribute to better understanding of the persistent black-white differences in mortality after breast cancer, and thus identify avenues to improve outcomes for all women with breast cancer.

Citation Format: Lawrence H. Kushi, Isaac J. Ergas, Janise M. Roh, Scarlett Lin Gomez, Marilyn L. Kwan, Catherine Thomsen, Song Yao, Christine B. Ambrosone. Disparities in breast cancer survivorship and outcomes [abstract]. In: Proceedings of the Tenth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2017 Sep 25-28; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2018;27(7 Suppl):Abstract nr IA27.