A recent report by DeSantis and colleagues from the American Cancer Society, summarized in this issue of The ASCO Post, presented breast cancer incidence and mortality data from an extensive analysis of the U.S. system of state-based tumor registries.1 The data showed that the incidence of breast cancer is increasing among non-Hispanic black women and has now approached and equaled that of white women. Historically, non-Hispanic black women had a lower incidence of breast cancer and higher mortality.
Impact of Tumor Characteristics
With mammography more evenly used across race/ethnic groups, the incidence of breast cancer has converged. However, the excess proportion of triple-negative breast cancer in black women is quite remarkable. These tumors with limited effective treatment options accounted for 10% of breast cancers among non-Hispanic white women yet 22% among non-Hispanic black women.
Detailed analysis of data from the National Comprehensive Cancer Network system has previously shown that tumor characteristics such as triple-negative status, as well as stage at diagnosis, are the predominant mediators for the excess mortality among black women. The distribution of tumor characteristics in these national data further supports the fact that these features likely account for a substantial portion of the mortality excess. Among postmenopausal women, obesity is directly related to poorer outcomes, and the distribution of obesity in the U.S. population, with higher prevalence among non-Hispanic black women, is an additional driver of the excess mortality.
Gap in Mortality
From 1995 onward, the decline in mortality among non-Hispanic black women has paralleled the decline observed among white women when absolute age-adjusted mortality rates are plotted. That is to say, the reduction over almost 20 years is approximately 10 deaths/100,000 women/year in both groups of women. Progress is being made, but the gap in mortality has not been reduced in absolute terms— Non-Hispanic black women have approximately 8 excess breast cancer deaths/100,000 women compared with non-Hispanic white women.
Substantial Variation Among States
The authors also summarized the evidence for mammography use as the likely equalizer to bring incidence rates together. Clearly, reproductive factors and obesity also contribute to the incidence of breast cancer. There remains substantial variation among states in the proportion of women aged > 45 years who report having a mammogram in the previous 2 years. Within the states with data specific for African American women, there is also substantial variation, with differences of up to 20% between states (68% up to 89%). Access to health services and their use for detection, diagnosis, and subsequent treatment are not equitably distributed within the United States. Rectifying this unequal access must be among our highest priorities to reduce disparities in breast cancer mortality.
Weight Gain and Obesity
The excess risk of triple-negative disease among non-Hispanic black women in these national data offers insight to one of the drivers for the excess mortality. Identifying more effective treatment strategies for these women remains a high priority. One might ask why there is an excess of estrogen receptor–negative or triple-negative disease.
A recent prospective cohort data analysis addressing short-term weight change showed that in both premenopausal and postmenopausal women, substantial short-term weight gain is directly associated with estrogen receptor–negative breast cancer. For example, in the Nurses’ Health Study, weight gain over 4 years was more strongly related to premenopausal breast cancer incidence than to postmenopausal breast cancer incidence. Among premenopausal women, short-term weight gain was associated with an increased risk of estrogen receptor–negative disease.2 European prospective data confirmed the greater adverse effect of short-term weight gain among premenopausal women.3
National data show higher levels of obesity among non-Hispanic black women at each obesity class level than among non-Hispanic white women. For example, National Health and Nutrition Examination Survey data from 2007– 2012 showed that body mass index was 30– 34.9 kg/m2 in 26.03% of non-Hispanic black women, 35– 39.9 kg/m2 in 13.45%, and ≥ 40 kg/m2 in 17.30%. In contrast, the corresponding figures for non-Hispanic white women were 17.58%, 9.37%, and 6.98%, respectively.4
Systematic review and meta-analysis of 82 studies revealed unequivocally that obesity at breast cancer diagnosis is significantly related to excess breast cancer mortality and total mortality.5 Greater weight gain during the premenopausal years in non-Hispanic black women resulted in the obesity prevalence numbers and drove the excess breast cancer risk. Given the direct relation of obesity to poor survival after breast cancer diagnosis, a far greater focus on maintaining a healthy weight across all racial/ethnic groups is essential to further reduce disparities in incidence and also improve outcomes after diagnosis. ■
Disclosure: Dr. Colditz reported no potential conflicts of interest.
References
1. DeSantis CE, Fedewa SA, Goding Sauer A, et al: Breast cancer statistics, 2015: Convergence of incidence rates between black and white women. CA Cancer J Clin. October 29, 2015 (early release online).
2. Rosner B, Eliassen AH, Toriola AT, et al: Short-term weight gain and breast cancer risk by hormone receptor classification among pre- and postmenopausal women. Breast Cancer Res Treat 150:643-653, 2015.
3. Emaus MJ, van Gils CH, Bakker MF, et al: Weight change in middle adulthood and breast cancer risk in the EPIC-PANACEA study. Int J Cancer 135:2887-2899, 2014.
4. Yang L, Colditz GA: Prevalence of overweight and obesity in the United States, 2007-2012. JAMA Intern Med 175:1412-1413, 2015.
5. Chan DS, Vieira AR, Aune D, et al: Body mass index and survival in women with breast cancer-systematic literature review and meta-analysis of 82 follow-up studies. Ann Oncol 25:1901-1914, 2014.
Dr. Colditz is Associate Director, Prevention and Control, Siteman Cancer Center, Washington University School of Medicine and Barnes-Jewish Hospital, St Louis.
