Breast cancer incidence rates increased in African American women from 2006 to 2010 and are now approaching the rates found in white women, according to a new analysis by American Cancer Society (ACS) researchers. The explanation for the rise in rates is unclear. 

Historically, white women have had the highest breast cancer incidence rates among women 40 years and older. Incidence rates for estrogen receptor-positive (ER+) breast cancers increased in the youngest white women, Hispanic women in their 60s, and all but the oldest African American women from 2006 to 2010. However, estrogen receptor-negative (ER­–) breast cancers declined among most age and racial/ethnic groups.

White women have the highest rates of ER+ breast cancer and African American women have the highest rates of ER– breast cancer in every age group. These differences may reflect racial variations in the prevalence of risk factors that differ by ER status. For example, reproductive history and obesity appear to be more strongly associated with ER+ breast cancer, whereas lower socioeconomic status is associated with an increased risk of ER– breast cancer.

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An estimated 232,340 new cases of invasive breast cancer and 39,620 breast cancer deaths will occur in US women in 2013. About eight in ten breast cancer cases and nearly nine in ten breast cancer deaths will occur in women 50 years and older.

A woman living in the United States had a 1-in-8 lifetime risk of developing breast cancer in 2013 compared to a 1-in-11 lifetime risk during the 1970s. Lifetime risk reflects the average probability of a breast cancer diagnosis from birth to death. Some of the increase in risk is due to improved detection of breast cancer from mammography screening as well as a longer life expectancy in women.

Breast cancer death rates have dropped by 34% since 1990 in all racial/ethnic groups except American Indians/Alaska Natives. The steady decline in breast cancer mortality has been attributed to improvements in early detection and treatment. But there are still survival disparities by race/ethnicity. African American women have the lowest breast cancer survival rate of any racial/ethnic group, and their death rate was 41% higher than the death rate in white women.

Differences in access to and use of early detection and treatment, and differences in tumor characteristics may contribute to the higher death rate in African American women, but much of the difference remains unexplained. These findings were published in CA: A Cancer Journal for Clinicians (doi: 10.3322/caac.21203).