Each year the American Cancer Society, Centers for Disease Control, National Cancer Institute and North American Association of Central Cancer Registries join forces to compile a report on national cancer statistics for the U.S. The recently released Annual Report to the Nation on the Status of Cancer 1975-2011 noted overall favorable trends in cancer incidence and mortality and for the first time included analyses by breast cancer subtype, race/ethnicity, socioeconomic status and geographic area.
Breast cancer continues to be the most common cancer in all U.S. women (excluding basal cell and squamous cell skin cancers and in situ carcinoma), and the second leading cause of cancer deaths, behind lung cancer. While the number of new breast cancer cases has been stable for more than two decades, mortality rates (deaths due to breast cancer) declined between 2002 and 2011, a trend that can be attributed in part to advances in early detection and treatment.
For the first time in the history of the Annual Report, the researchers were able to break down breast cancer statistics based on molecular subtype using national data collected on hormone receptor and HER2 status.
Breast cancers can be classified into four broad categories, although there is increasing effort to further subcategorize breast cancers based on new pathways that can be targeted for therapy. The four major subtypes are based on the presence or absence of hormone receptors (HR) for estrogen and/or progesterone and of the growth factor receptor, HER2. They are:
Luminal A: HR+/HER2- (Cancer cells have hormone receptors but lack high amounts of HER2.)Luminal B: HR+/HER2+ (Cancer cells have hormone receptors and abnormally high amounts of HER2.)HER2 enriched: HR-/HER2+ (Cancer cells do not have hormone receptors, but have abnormally high levels of HER2.)Triple negative (includes basal-like): HR-/HER2- (Cancer cells do not have the hormone receptors or HER2.)
The testing of breast tumors for both hormone receptor and HER2 status has been routine in clinical care for nearly a decade and is used to guide treatment and management decisions. Targeted therapies such as tamoxifen and Herceptin® are widely used to treat breast cancers that have the estrogen or HER2 receptor, respectively, but there are no targeted therapies for triple negative breast cancer at the present time. Patients should be aware of the type of breast cancer they have to better understand what is guiding their treatment and the clinical implications of their diagnosis.
Breast cancer incidence by subtype
According to the report and in agreement with previous smaller studies, the luminal A subtype of breast cancer (HR+/HER2-), typically the least aggressive form of breast cancer comprises over 70 percent of all breast cancer cases. Triple negative breast cancer (HR-/HER2-), an aggressive form of the disease, accounts for 13 percent of all breast cancers, while luminal B and HER2-enriched (HR-/HER2+) breast cancers make up approximately 10 and 5 percent, respectively, of all breast cancers. The report also noted that most breast cancers of all subtype are diagnosed at an early stage, likely due in part to advances in screening, and an important factor in the decline in mortality rates from breast cancer in the U.S.
Trends by race/ethnicity
While luminal A breast cancer is the most common form of the disease across all races and ethnicities, it is highest among whites compared to other groups. Triple negative breast cancer is highest among blacks in which it is the second most common breast cancer– occurring at two to three times the incidence rate of white, Hispanic or Asian women.
While the incidence of breast cancer overall has been stable in the decade between 2002 and 2011, incidence rates in black women have increased. Black women are also more likely to be diagnosed with advanced-stage breast cancer, regardless of subtype and in spite of increased mammography screening in the group. These trends corresponded to higher mortality rates in black women compared to whites, Hispanics and Asian-Americans, and demonstrate clear population differences in breast cancer subtypes.
“BCRF has been at the forefront in support innovative research that gets to the root of disparities in breast cancer outcomes by supporting our work across the African Diaspora,” comments Funmi Olopade . “Not only are we discovering the root causes of breast cancer among women of African ancestry, we are also developing the necessary infrastructure to ensure that these women can receive potentially life saving treatments no matter where they live.”
By providing information on the distribution of breast cancer by subtype, this year’s Annual Report can help doctors and researchers categorize patients to improve screening, prevention and treatment recommendations, and is in line with the goals of the precision medicine initiative announced by President Obama earlier this year.
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