Lawrence H. Kushi, ScD

Even with equivalent access to care, black patients with breast cancer may fare worse than white patients with breast cancer, according to Lawrence H. Kushi, ScD, Director of Scientific Policy at the Kaiser Permanente Northern California Division of Research in Oakland.

“Accounting for socioeconomic status seems to have the greatest individual impact on explaining disparities in mortality rates,” he said at the 2017 American Association for Cancer Research (AACR) Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved in Atlanta.¹

Well-Established Disparities

In the United States, women of European ancestry have historically had the highest incidence of breast cancer compared with those of other racial/ethnic groups. In recent years, the disparity in the incidence of breast cancer between white and black women has narrowed, but once diagnosed with breast cancer, black women have poorer survival.

The most recent “Annual Report to the Nation on the Status of Cancer” cited a higher age- and stage-adjusted relative mortality risk after breast cancer of 71% for non-Hispanic blacks compared with non-Hispanic whites, based on nationwide cancer registry data from 2006 to 2013.²

The reasons for these disparities in outcomes after breast cancer are complex, but could enrollment in Kaiser Permanente—with essentially equal access to health care—attenuate these racial/ethnic differences in outcomes? An attempt to answer this question was the impetus behind the Pathways Study, led by Dr. Kushi.

The Pathways Study

This ongoing, prospective cohort study was designed to investigate the effects of lifestyle, clinical, molecular, and contextual factors on breast cancer prognosis. Recruitment from the Kaiser Permanente health-care system began in 2006 and ended in 2013, with 4,505 multiethnic women diagnosed with breast cancer enrolled. The last date of complete follow-up for major endpoints was September 20, 2016.

According to Dr. Kushi, preliminary analyses in the larger population of 11,176 women who were diagnosed with invasive breast cancer in Kaiser Permanente Northern California 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, black women had a 59% increased relative mortality risk compared with white women, after adjusting for age and stage of cancer at diagnosis.

Results were comparable among women enrolled in the Pathways Study. After 538 total deaths, black women had an 81% increased relative mortality risk compared with white women after adjusting for age and stage. “You might have expected more of an attenuation [between black and white women], but we don’t actually see that in our cohort,” he noted. “But if we take into account some of the information that exists in the cancer registry, adjusting for age, stage, tumor size, and receptor status, there was a slight decrease in risk for black women.” Adjusting for these factors caused the increased risk for black women to drop from 81% to 60%, and adding in treatment status furthered this attenuation.

Body mass index (BMI) and physical activity had a minimal impact, despite their strong associations with mortality. However, socioeconomic status had the most substantial impact on diminishing the magnitude of these disparities, decreasing the risk from 45%—after adjusting for age, stage, tumor variant, treatment status, and BMI—to 24% with the addition of socioeconomic status. Similar black-white differences were also seen in regard to the risk of recurrence in the Pathways Study cohort, although they were less pronounced.

Dr. Kushi and his colleagues found that the disparities in mortality rates within the Pathways cohort—and within Kaiser Permanente generally—were similar to those seen nationwide. Despite equivalent access to care, black patients fared worse than white patients. Accounting for diagnostic and prognostic factors that are widely available in tumor registries, such as tumor size, receptor status, and treatment variables, attenuate, but do not eliminate, these disparities, he added.

Possible Deep-Seated Inequities

In 2003, the Institute of Medicine’s (IOM) Committee on Understanding and Eliminating Racial and Ethnic Disparities in Health Care argued that racial and ethnic minorities tended to receive a lower quality of health care than non-minorities, even when access-related factors such as patients’ insurance status and income are controlled.³ “That’s, in fact, what we’ve observed at Kaiser Permanente in breast cancer,” said Dr. Kushi. The IOM report continued to state that the sources of these disparities are complex, are rooted in historic and contemporary inequities, and may involve many participants at several levels.

“When thinking about different racial/ethnic groups, some of these differences might be clinically appropriate, ie, comorbidities and contraindications,” he added. “But there may be other things going on that are not appropriate, and that’s really what we want to try to minimize.”

Next Steps

The next steps in the Pathways Study include more detailed analyses of medical care factors such as chemotherapy dosing, comorbidities, care coordination and guideline-concordant care, as well as further investigation into psychosocial and contextual factors and the differences between self-identified race/ethnicity vs genetic ancestry.

According to Dr. Kushi, “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.” ■

DISCLOSURE: Dr. Kushi reported no conflicts of interest.

REFERENCES

1. Kushi LH: Disparities in breast cancer survivorship and outcomes. 2017 AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved. Presented September 27, 2017.

2. Jemal A, Ward EM, Johnson CJ, et al: Annual Report to the Nation on the Status of Cancer, 1975-2014, Featuring Survival. J Natl Cancer Inst 109:djx030, 2017.

3. Smedley BD, Stith AY, Nelson AR, eds: Unequal Treatment: Confronting Racial and Ethnic Disparities in Health Care. Committee on Understanding and Eliminating Racial and Ethnic Disparities in Health Care, Institute of Medicine, Washington, DC, National Academies Press, 2003.