A study suggests age-specific incidences of breast cancer subtypes vary by race, showing that the differences by race occur only when tumor subtypes are grouped together.
The study was published in the Journal of the National Cancer Institute. The study aimed to help expand our understanding of the apparent differences in breast cancer rates among ethnically diverse women of various age groups.
Past studies have shown a Black-White crossover in breast cancer diagnoses: Breast cancer occurs more often in Black than White women before age 40, but more often in White than Black women after age 40.
Background and Reason for the Study
Researchers identified the Black-White crossover in the 1980s. Yet, this trend was noted without considering breast cancer subtype.
Subtypes are classified based on tumor expression of three receptors: The estrogen receptor (ER), progesterone receptor (PR) and HER2. When a tumor tests negative for ER, PR and HER2, it is called triple-negative breast cancer. Understanding subtypes is important in determining risk factors, treatment and outcome.
Breast cancer rates specific to subtypes vary by race. For example, higher rates of triple-negative breast cancer occur among Black women, while White women tend to have higher rates of ER-positive breast cancer.
Investigators wanted to know if the Black-White crossover or any age-related crossovers between racial groups occurred when breast cancer subtypes were considered separately.
Study Structure and Findings
Investigators reviewed 76,227 cases of invasive breast cancer among women diagnosed between 2006 and 2009 from the California Cancer Registry’s records.
No age-related crossover was observed across all races, including among Black vs. White women, for any of the subtypes. Breast cancer rates for women younger than age 45 at diagnosis were highest among Black than White women. Rates were higher among White than Black women for those over age 50 at diagnosis. Hispanic and Asian women experienced lower rates at all ages of diagnosis compared with Black and White women.
There were no differences in age based on HER2 status, whether the cancer was ER/PR positive or not.
The differences in rates between racial and ethnic groups were more noticeable in terms of breast cancer subtype than age.
The HR+/HER2- tumor had the highest incidence rates of all subtypes at all ages of diagnosis. White women had statistically significant (unlikely to have happened by chance) higher rates of HR+/HER2- breast cancer than any other race or ethnic group at all ages, most notably after 45. White and Asian women had more than six times as many HR+/HER2- tumors vs. triple-negative tumors than Latina and Black women.
There was no noticeable statistically significant racial or ethnic difference in rates of the HR+/HER2+ tumor.
Investigators found that Asian women between ages 40-64 had higher rates of HR-/HER2+ breast cancer compared with White women.
Differences in breast cancer rates among race were larger for triple-negative disease compared with any other breast cancer subtype. Black women had statistically significant higher rates of triple-negative breast cancer than women of other races and ethnicities at all ages.
What This Means for You
This study focuses the conversation about breast cancer subtypes (i.e., triple-negative breast cancer) and ethnic/racial differences. This study scientifically confirmed that triple-negative breast cancer disproportionately affects Black and younger women. Talk with your doctor to learn about your age- and race-related risks and treatment options specific to your unique background and tumor subtype.
In summary, the investigators found no evidence of the Black-White crossover among women diagnosed with each specific tumor subtype. Therefore, this study suggests high rates of triple-negative breast cancer in Black and younger women and high rates of HR+/HER2- breast cancer in older White women best explain the ethnic – age differences in breast cancer incidence rate (how much the illness occurs per 100,000 persons). These findings suggest continued research must focus on identifying the causes of, and best treatment for, specific tumor subtypes to produce better outcomes for high-risk groups of women.
Clarke CA, Keegan TH, Yang J et al. Age-specific incidences of breast cancer subtypes: understanding the Black-White crossover. Journal of the National Cancer Institute. 2012;104:1094-1101.