Breast cancer rates among black women increased from 2008 to 2012 in the United States, eliminating a the gap that had existed for decades between black and white women, according to a study from the American Cancer Society (ACS).
"Although white women have historically had higher incidence rates than black women, in 2012, the rates converged," write the study authors, led by Carol DeSantis, MPH, an ACS epidemiologist.
In 2012, the breast cancer incidence rates were 135.0 per 100,000 white women and 135.2 per 100,000 black women.
Rates had been lower among black women since at least 1975, the authors report. The data from the Surveillance, Epidemiology, and End Results (SEER) program of the National Cancer Institute.
From 2008 to 2012, rates for black women have risen 0.4% per year, whereas rates for white women have been "relatively stable," resulting in the convergence, according to the authors.
The data were published online today in CA: A Cancer Journal for Clinicians.
DeSantis was involved in previous research that showed that the increase in incidence rates in black women has been driven by increases in estrogen-receptor-positive breast cancers (CA Cancer J Clin. 2014;64:52-62).
But what biologic or social factors are behind the increase?
"I can't say for sure what is driving the increase in breast cancer incidence in black women but not white women," DeSantis told Medscape Medical News. However, it probably is not increased detection. "Screening rates are similar between black and white women and have been pretty stable over the past decade," she said.
The prevalence of obesity in black women has continued to increase, but it has leveled off for white women.
"I think it is more likely that obesity trends are at least partially responsible. In the United States, the prevalence of obesity in black women has continued to increase, but it has leveled off for white women," she said.
Obesity is a known risk factor for postmenopausal breast cancer, DeSantis and her coauthors point out.
In black women, the obesity rate was 39% from 1999 to 2002, 49% from 2003 to 2006, and rose to 58% from 2009 to 2012, according to a recent study (Cancer Epidemiol Biomarkers Prev. 2015;24:637-652).
Notably, breast cancer incidence rates are higher in black women than in white women in seven states (Alabama, Kentucky, Louisiana, Mississippi, Missouri, Oklahoma, and Tennessee).
The difference in breast cancer deaths has been well recognized. "The mortality disparity between black and white women nationwide has continued to widen; and, by 2012, death rates were 42% higher in black women than in white women," DeSantis's team writes.
Black women have the highest rate of breast cancer deaths of any racial/ethnic group in the United States.
Overall, however, breast cancer death rates decreased by 36% from 1989 to 2012 in the United States. This means that 249,000 breast cancer deaths were averted during this period, the authors note. The decrease in death rates was evident in all racial/ethnic groups except American Indians/Alaska Natives.
The authors have disclosed no relevant financial relationships.
CA Cancer J Clin. Published online October 29, 2015.
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