Do breast quadrants explain racial disparities in breast cancer outcomes?
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Tumors of the inner quadrants of the breast are associated with poorer survival than those of the upper-outer quadrant. It is unknown whether racial differences in breast cancer outcomes are modified by breast quadrant, in addition to comparisons among Asian subgroups.
Using the Surveillance, Epidemiology, and End Results database, we analyzed data among women diagnosed with non-metastatic invasive breast cancer between 1990 and 2014. We performed Cox proportional hazards regression models to assess the associations of race with breast cancer-specific survival and overall survival, stratified by breast quadrants. The models were adjusted for age, year of the diagnosis, tumor size, grade, histological type, tumor laterality, lymph node, estrogen receptor, progesterone receptor, and treatments.
Among 454,154 patients (73.0% White, 10.0% Black, 7.8% Asian/PI, and 9.2% Hispanic), 54.3% had tumors diagnosed in the upper-outer quadrant of the breast. Asian/PI women were more likely than White to have tumors diagnosed in the nipple/central portion of the breast and were less likely to have diagnosed in the upper-outer quadrant (P < 0.001), despite a similar distribution of breast quadrant between Black, Hispanic, and White women. Compared with White women, the multivariable-adjusted hazard ratios of breast cancer-specific mortality were 1.41 (95% CI 1.37–1.44) in Black women, 0.82 (95% CI 0.79–0.85) in Asian women, and 1.05 (95% CI 1.02–1.09) in Hispanic women. Among Asian subgroups, Japanese American women had a lower risk of breast cancer-specific mortality (HR = 0.68, 95% CI 0.62–0.74) compared with White women. Overall survival was similar to breast cancer-specific survival in each race group. The race-associated risks did not vary significantly by breast quadrants for breast cancer-specific mortality and all-cause mortality.
Differences in breast cancer survival by race could not be attributed to tumor locations. Understanding the cultural, biological, and lifestyle factors that vary between White, African American, and ethnic subgroups of Asian American women may help explain these survival differences.
KeywordsBreast cancer Race Breast quadrant Primary tumor site Survival
Breast cancer-specific mortality
Breast cancer-specific survival
Not otherwise specified
Surveillance, Epidemiology, and End Results
Dr. Han was supported by foundations from Barnes-Jewish Hospital and Breast Cancer Research Foundation (award ID: BCRF-17-028). Dr. Colditz is supported by the Breast Cancer Research Foundation. Drs. Moore, Langston, Fuzzell, Khan, and Lewis were supported by the Washington University School of Medicine, Public Health Sciences Division Postdoctoral Training in Cancer Prevention and Control, and a training grant from the National Cancer Institute of the National Institutes of Health under award number T32CA190194. YL is supported by an American Cancer Society—Denim Days Research Scholar Grant (RSG-18-116-01-CPHPS) and the National Cancer Institute (R01CA215418). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
This article does not contain any studies with human participants or animals performed by any of the authors.
As this study is based on a publicly available database without identifying patient information, informed consent was not needed.
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