US Breast Cancer Rates No Longer Falling

Janis C. Kelly

March 08, 2011

March 8, 2011 — The sharp decline in breast cancer incidence rates seen in the United States in 2003 has leveled off. Incidence rates are no longer decreasing, and in fact might be increasing in some groups.

The findings come from a study conducted by researchers from the American Cancer Society and the National Cancer Institute (NCI), published online February 28 in Cancer Epidemiology, Biomarkers & Prevention.

The sharp drop in breast cancer incidence rates seen in non-Hispanic white women in the United States in 2003 appears to be largely due to the abrupt decline in postmenopausal hormone therapy use after the Women's Health Initiative 2002 report on the adverse effects of combined hormone therapy use, the authors note. Breast cancer incidence has now leveled off, and might even be rising in some subgroups, particular in tandem with obesity rates, they add.

To determine whether the decline in breast cancer incidence continued after 2003, Carol DeSantis, MPH, from surveillance research at the American Cancer Society, and colleagues at the NCI analyzed data from 12 registries in the Surveillance, Epidemiology and End Results (SEER) database on female invasive breast cancer incidence for 2000 to 2007.

Ms. DeSantis told Medscape Medical News that her group's key findings were:

  • no significant changes in overall breast cancer incidence in non-Hispanic white or black women or in Hispanic women from 2003 to 2007

  • a slight (2.7% per year) increase in estrogen receptor (ER)-positive cancers and a decrease in ER-negative cancers in non-Hispanic white women 40 to 49 years of age

  • an annual 5.24% increase in ER-positive breast cancers in black women 40 to 49 years of age

  • a slight decrease in ER-negative cancers in non-Hispanic white women 60 to 69 years of age

  • a continued decline in postmenopausal hormone use in all age groups.

"I think it is striking that there are higher rates of ER-positive breast cancer in whites in every age group and, likewise, higher rates of ER-negative disease in blacks. Although it appears that incidence rates have stabilized for now, I am interested to see the patterns that emerge as new data become available," Ms. DeSantis said.

According to Ms. DeSantis, several factors might have contributed to the stabilization in breast cancer incidence rates among non-Hispanic white women in the United States. Postmenopausal hormone therapy delays the diagnosis of breast cancer, she explained; although its use continued to decline through 2008, the levels of use after 2003 might not have been large enough to continue delaying diagnoses.

Hormone therapy also increases breast density and interferes with the sensitivity of mammography. Without the influence of hormone therapy, mammography might have been detecting more breast cancers. The stabilization might also partly reflect the relatively stable rates of screening mammography in the United States since 2000.

"I think the 2 main drivers of breast cancer incidence rates over the last 3 decades were increases in mammography screening and postmenopausal hormone use. Mammography use appears to have plateaued, and the prevalence of hormone therapy use is now quite low. It remains to be seen if incidence rates continue to remain level," said Ms. DeSantis.

The researchers suspect that the increased ER-positive and ER-negative breast cancer rates in black women "reflect trends in the prevalence of obesity, which increased through the mid-2000s."

"A woman's best strategy is to get regular mammograms and reduce her known risk factors as much as possible (i.e., avoid weight gain and obesity, engage in regular physical activity, minimize alcohol intake and the use of postmenopausal hormone therapy)," Ms. DeSantis said.

Study Adds Convincing Evidence

Medscape Medical News sought independent comment from Prithwish De, PhD, an epidemiologist from the Canadian Cancer Society in Toronto, Ontario, who has analyzed breast cancer incidence and hormone therapy in Canadian women.

"This new study adds more convincing evidence about the role of hormone replacement therapy [HRT] in breast cancer," Dr. De said. "It reinforces findings from numerous countries about the relatively quick and dramatic decline in the breast cancer incidence rate following a decline in HRT use. The specific data on trends by estrogen-receptor status and by ethnic group also help clarify the types of breast cancer and the population subgroups that are most affected."

Dr. De added that "the rising trend in the breast cancer incidence rate following the steep decline helps reinforce the hypothesis that HRT plays a role in promoting growth of occult tumors (i.e., tumors that are difficult to detect). In our article in [the Journal of the National Cancer Institute] last fall [2010;102:1489-1495], we reported on this rebound, which started in 2005 in Canada (although we weren't able to specifically comment about the receptor status of breast cancer cases or about specific population subgroups). We suggested that the rise likely reflects the continued impact of other prominent risk factors (such as age) on the breast cancer incidence trend in the absence of HRT use or changes in mammography usage rates. However, more research to collect longer-term data is needed to confirm this renewed upward trend. It will also be important to monitor breast cancer incidence trends in other regions of the world where HRT use has experienced a similar change."

Ms. DeSantis and Dr. De have disclosed no relevant financial relationships.

Cancer Epidemiol Biomarkers Prev. Published online February 28, 2011. Abstract

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