Hormone Replacement Therapy Likely to Increase Risk of Breast Cancer

Previous studies have revealed that Hormone Replacement Therapy (HRT) increases the risk for breast cancer in healthy women, but until now, the effects of HRT on breast cancer survivors was not known. However, the results of a clinical trial conducted by Lars Holmberg, M.D., Ph.D. and colleagues, of King's College London, indicate that survivors were 14 percent more likely to have a recurrence if they use HRT. These results will be published in the April 2nd issue of the Journal of the National Cancer Institute.

A total of 442 Cancer survivors participated in the clinical trial, dubbed HABITS (Hormonal Replacement After Breast Cancer —Is It Safe?). The trial was stopped in 2003 after concerns arose regarding an increased risk of breast cancer recurring for women on hormone therapy. Women in the trial had both estrogen receptor-positive and estrogen receptor-negative cancers. (The hormone estrogen fuels estrogen receptor-positive cancer).

The research team examined breast cancer rates for trial participants after an average follow-up of four years. It was found that 17 percent of 221 women who took HRT after breast cancer developed a recurrence of the disease, compared to only 8 percent of 221 women who did not take the drugs. The probable rate of recurrence after five years was 22 percent for HRT users and 10 percent for non-users, which is a total increase in risk of 14 percent. The study did not determine if taking HRT increases the risk of dying from breast cancer.

Researchers conclude in the report that: The results indicate a substantial risk for a new breast cancer event among breast cancer survivors using hormone-replacement therapy; and, that the results further suggest that hormone therapy not only induces and promotes breast cancer but may also stimulate the growth of tumor microdeposits in breast cancer survivors.

HRT was used widely among menopausal women until 2002, following a major study that found the use of HRT could increase the risk for developing breast and ovarian cancer. It was also shown that HRT could increase the likelihood of strokes and other serious conditions. At that time, millions of women immediately discontinued the use of HRT drugs.

Physicians continue to urge women who need HRT drugs for the relief of serious menopause symptoms such as hot flashes and vaginal dryness to consider taking them, particularly as lower-dose therapies are now available that can be taken for short durations.

In an accompanying editorial to the report, Kathy I. Pritchard, M.D., of the Sunnybrook Odette Cancer Center in Toronto noted that although a randomized study from Stockholm found no increased risk of breast cancer recurrence among breast cancer survivors taking HRT, there may be key differences between this trial and the HABITS study, including the dosing schedule, the duration of treatment, and the type of hormones used (synthetic versus natural compounds). Those differences leave open several questions.

However, in consideration of the most recent data, Pritchard wrote, “Although randomized data concerning use of HRT for symptomatic intervention in breast cancer survivors are still sparse, it seems that the harmful side effects of HRT have finally been clearly demonstrated.”