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Hormone replacement therapy and breast cancer risk further defined

Kathleen Blanchard's picture

Researchers have further defined the risk of breast cancer associated with taking hormone replacement therapy. New findings from an almost ten year study show hormone replacement therapy and the risk of breast cancer varies among women.

Despite the variances found, women should understand the risk of breast cancer from hormone replacement does exist.

Susan Hankinson, Sc.D., professor of medicine at Harvard Medical School and a senior editor of Cancer Epidemiology, Biomarkers & Prevention says, "There is an increased risk of breast cancer from hormone use, and further studies will address the question of how specific that risk is", despite the variances found in the study. The findings come from an analysis of the California Teachers Study that included 2,857 women using hormone replacement therapy

Hormone replacement therapy and breast cancer risk strongest with low BMI and combined hormones

The analysis showed that women who used a combination of estrogen plus progestin for 15 years or more had an 83 percent increased chance of developing breast cancer.

Combined hormone replacement therapy with low body mass index (less than 25) was associated with the greatest risk of breast cancer. Women with BMI less than 30 were also at increased risk.

High BMI (greater than 30) and combined hormone replacement therapy did not increase breast cancer risk any further, despite past findings that obesity alone is a risk factor for developing the disease.

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Estrogen therapy alone less risky for breast cancer

Women taking estrogen replacement for menopausal symptoms had the lowest risk of breast cancer. For women taking estrogen for 15 years or more the risk of cancer was nineteen percent, compared to the 83 percent increased risk found with combination hormones that was also influenced by body mass index.

Breast cancer type also linked to hormone replacement therapy

The analysis also showed hormone replacement therapy was linked to tumors that were positive for both estrogen and progestin receptors. The weakest link was found with HER2 negative tumors.

The study authors say hormone replacement therapy still increases the risks of breast cancer, but varies according to personal characteristics.

Tanmai Saxena, M.D./Ph.D who is a student at the Keck School of Medicine at the University of Southern California where the analysis was conducted explains, "The benefits of hormone therapy for relief of postmenopausal symptoms among women are clear, but the risks are more complicated than we had previously thought."

The findings suggest a personalized risk benefit analysis for women considering taking hormone replacement therapy. Hormones taken for relief of menopause symptoms do increase the risk of breast cancer, especially with combined estrogen and progestin for 15 years or more. The risk was also dependent on breast cancer subtype. Though the analysis further defines a woman's individual risk of hormone therapy and breast cancer, there are still unanswered questions.

Cancer Epidemiology, Biomarkers & Prevention: doi:10.1158/1055-9965.EPI-10-0162