When it was discovered in 2002 that hormone replacement therapy (HRT) increased the likelihood of developing breast cancer and coronary heart disease, many women stopped taking the estrogen-based medications that eased the discomforts of menopause.  The overall number of breast cancer diagnoses declined in the following years, too, but a recent study conducted by researchers at the University of Chicago Medical Center shows the rate of decline varies according to ethnicity.

When postmenopausal Caucasian women stopped HRT, the rate of cancer within this group dropped by 2% or more for every three-month period from mid-2002 until becoming stabilized in 2004.  There was little or no such decline in the number of breast cancer cases in women of African-American descent.

Invasive cancer, which affects the tissue surrounding a cancerous lesion, occurred in about 86 per 100,000 women each quarter of the year in the early part of 2002, when HRT was common.  This rate dropped to 74 per 100,000 by the beginning of 2004.

The 2002 rate of breast cancer in African-American women was 71 per 100,000 per quarter and it remained stable until 2004.  Asian women saw a slight drop in numbers but the rate of invasive breast cancer in these women remained fairly stable at about 65 per 100,000.  There was no decline indicated for Native American women but their rate of invasive breast cancer is usually rather low, 33 per 100,000.

The majority of breast cancers, about 80%, that develop in Caucasian women is of the estrogen receptor positive type, meaning it requires estrogen for growth.  This type cancer accounts for only about 60% of the breast cancers in African-American women but the rate drops to only about 30% when the African-American woman is of Nigerian ancestry.

The study, led by Dezheng Huo, PhD, assistant professor of health studies at the University of Chicago Medical Center, thinks the prevalence of mammographies in recent years may account for rising numbers of breast cancer diagnoses during the late 1990s.  For the study, Huo’s research team analyzed data on women 50 to 69 years old that was taken from 17 extensive cancer registries.  The registries account for about 26% of the nation’s population.

The findings of this study point to the very real possibility that estrogen and progesterone are metabolized differently according to genetic heritage.  Also suggested is that estrogen may play the role of promoter in breast cancer instead of being the cause itself.

The findings of this study are being presented at the annual 2008 meeting of the American Association for Cancer Research in San Diego.  Funding was provided by a Breast Cancer SPORE grant awarded by the National Cancer Institute.