Among women with early-stage breast cancer—diagnosed due to early awareness, physician or self-examination, or mammography—“there was still a toll from breast cancer, and that toll seemed to be disproportionately felt among women of black race.”

That’s the conclusion of an observational study of more than 450,000 women in the United States who were diagnosed with invasive breast cancer from 2004 to 2011 and followed for 7 years.

The goal of the study, published in The Journal of the American Medical Association (JAMA) on January 13, 2015, was to determine whether factors that predict diagnosis of early-stage breast cancers could be identified and, of those, “whether ethnic differences may be better explained by early detection or by intrinsic biological differences in tumor aggressiveness,” such as “lymph node metastasis, distant metastasis, and triple-negative behavior of tumors.”

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Compared with white women, Hispanic women, and Asian women, and black women did relatively poorly for all variables examined: they were less likely to have their cancer diagnosed at an early stage and had poorer survival.

However, to a large degree, these differences were not due to lack of access to care or awareness, said Steven Narod, MD, Canada Research Chair in Breast Cancer, Women’s College Research Institute and the Dalla Lana School of Public Health at the University of Toronto in Toronto, Ontario, Canada, the study’s corresponding author.

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Rather, they “seemed largely to be due to intrinsic or biological propensity of small breast cancers to spread,” said Dr. Narod in an interview with JAMA about the study.

“A woman with a 2 cm breast cancer who was black was more likely to present with a node-positive breast cancer or a metastatic breast cancer than a white woman with a similar breast cancer of 2 cm.”