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New Data Indicates Combined Hormone Therapy Ups Breast Cancer Risk

The review of new data, recently published in the Journal of the National Cancer Institute, provides further strength to the argument that hormone replacement therapy (HRT) increases the risk of developing breast cancer among postmenopausal women. However, this risk is largely dependent upon the timing of HRT use in relation to when menopause begins.

Menopause is cessation of a woman’s menstrual cycle which occurs later in life. It is associated with low levels of the female hormones estrogen and progestin. The low levels of these hormones can cause symptoms in postmenopausal women that range from mild discomfort to debilitation of normal life.

To alleviate the severity of symptoms caused by menopause, women may be treated with hormone replacement therapy (HRT) in which estrogen and/or progestin are given to the patients.

However, data from large clinical studies has indicated a possible increased risk of breast cancer associated with the use of HRT. Researchers continue to evaluate data to further understand this risk.

The Women’s Health Initiative (WHI), one of the largest clinical trials ever to assess HRT and breast cancer risk, initially raised awareness to the idea that HRT may increase breast cancer risk. Following the release of the WHI results, HRT use fell dramatically among postmenopausal women. Since then, researchers have continued to explore possible variables that may further increase or decrease a woman’s risk of breast cancer in association to HRT.

Researchers recently conducted a longer-term analysis of data from obtained from part of the WHI. The women included in the data were not part of the clinical trial portion of the WHI, but part of the observational portion of WHI. This data include nearly 42,000 postmenopausal women who were followed for more than 11 years.

More than 25,000 of these women did not take any HRT, while more than 16,000 took combined HRT, which means HRT included both estrogen and progestin. This analysis only included women taking combined HRT, not estrogen-only HRT.

The risk of developing breast cancer was increased among women taking HRT versus those who did not take HRT.
This risk was significantly higher among women who started taking HRT closest to the beginning of menopause compared with those who started taking HRT later into menopause.
The researchers speculate that women may still produce small amounts of hormones towards the beginning of menopause and the addition of HRT provides high enough hormone levels to stimulate breast cancer development.
The researchers stated that, according to these results, “estrogen plus progestin use is associated with increased breast cancer incidence.” However, HRT has been associated with some positive health benefits, so it is important for postmenopausal women considering HRT for symptom control to discuss all risks and benefits of HRT in their individual situation.

Reference: Chlebowski R, Manson J, Anderson G, et al. Estrogen Plus Progestin and Breast Cancer Incidence and Mortality in the Women’s Health Initiative Observational Study. Journal of the National Cancer Institute. First published online: March 20, 2013. DOI: 10.1093/jnci/djt043.