(ChemotherapyAdvisor) – Age-specific incidences of breast cancer subtypes vary by race, according to a team of US-based researchers. This conclusion is based on a study entitled “Age-Specific Incidence of Breast Cancer Subtypes: Understanding the Black–White Crossover,” which was published in the Journal of the National Cancer Institute on July 18.

The investigators aimed to determine if age-specific incidences of breast cancer subtypes vary by race and ethnicity. Previous studies have demonstrated that the incidence of breast cancer is higher among black women than white women before age 40 years, and that this trend reverses after age 40 years (known as the black–white crossover). Using population-based data, the investigators classified 91, 908 invasive breast cancers using, as molecular classifiers, the expression of estrogen receptor (ER) and progesterone receptor (PR)—collectively known as hormone receptor (HR)—and human epidermal growth factor receptor 2 (HER2).

In contrast to previous studies, the investigators in this study did not observe an age-related black–white crossover. “Compared with white women, black women had statistically significantly higher rates of triple-negative (ER, PR, and HER2 negative) breast cancer at all ages but statistically significantly lower rates of HR+/HER2 breast cancers after age 35 years (all P<.05),” they reported. “The age-specific incidence of HR+/HER2+ and HR/HER2+ subtypes did not vary markedly between white and black women.”

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Based on the results of this study, it became apparent to the investigators that the oft-reported black–white crossover in breast cancer incidence must only occur when all breast cancer subtypes enter into the calculation of incidence. The investigators posited the main factor that leads to this phenomenon could be, compared with white women, black women have the higher rate of triple-negative breast cancers and lower rates of HR+/HER2 breast cancers.