CLEVELAND, June 26 (MedPage Today) -- The nationwide drop in breast cancer rates linked to the decline of hormone replacement therapy tracks both income and locale, with more significant reductions observed in affluent, urban areas, a new study shows.
From 2001 to 2004 the overall incidence of invasive breast cancer fell by 13.8% in urban areas, versus a 7.5% decline in rural areas, according to Amelia K. Hausauer, PhD, of the Northern California Cancer Center in Fremont, and colleagues.
Likewise, invasive breast cancer rates fell by 13% in neighborhoods in high-income counties, compared to a 9.6% decline in poor counties, although the intracounty changes from baseline were significant in each case (P<0.001),>
"Breast cancer incidence trends for rural counties, which peaked in 1999 and then declined steadily, differed from those in observed in urban counties, where rates fell most dramatically after 2002," they remarked.
This distinctly different pattern of decline is "consistent with the changing pattern of [hormone therapy] prevalence and cessation or noninitiation," the authors concluded.
The use of hormone replacement increased steadily until 1999, when it peaked at 92 million prescriptions. It remained steady until the watershed moment of July 9, 2002.
On that day, the National Health Lung and Blood Institute announced that it had pulled the plug on a study investigating health claims for hormone replacement (estrogen-progestin) in 14,749 healthy women, when it discovered that the five-year incidence of breast cancer was significantly higher among women assigned to hormone therapy compared with those taking placebo.
Following that announcement, there was a significant decline in the use of hormone therapy, and in the past year a number of studies have reported a subsequent decline in breast cancer incidence.
Dr. Hausauer and colleagues analyzed data from 29 population-based cancer registries that participate in the North American Association of Central Cancer Registries.
According to the registry, there were 475,523 cases of invasive breast cancer and 111,885 cases of in situ breast cancer diagnosed between from 1997 through 2004.
The researchers limited their analysis to cases reported in non-Hispanic white women age 50 to 74, and stratified the findings by counties of residence at the time of diagnosis. The counties were further stratified by rural/urban status and by income.
Among the findings:
- Breast cancer was most likely be diagnosed in urban areas, with 85.7% of invasive breast cancers and 88% of in situ breast cancer diagnosed in cities versus suburban or rural communities.
- From 2001 to 2004 the breast cancer rate declined by 13.8% in urban areas (P<0.001 p="0.02).
Although hormone therapy seems a likely explanation for the declines seen in this analysis, the authors cautioned that some of the change -- especially the slow but steady decline observed in rural communities -- could be explained by "saturation of or decreases in mammographic screening."
The authors said their report was limited by the lack of individual socioeconomic information, and a lack of adjustment for possible delays in reporting. Moreover, the authors could not stratify the results by gene-expression subtype or by hormone receptor status.
Dr. Hausauer declared that she had no competing interests.
The registries used in the study were supported by individual states with additional funding from the CDC, and, in some cases, the National Cancer Institute's SEER Program.
Primary source: BMC Medicine Source reference: Hausauer AK, et al "Recent trends in breast cancer incidence in US white women by county-level urban/rural and poverty status" BMC Med 2009.
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