Estrogen-plus-progestin hormone replacement therapy (HRT) not only increases a woman’s risk of developing invasive breast cancer, but it also raises her chances of dying from it or from any other cause after being diagnosed with breast cancer. This was the finding of a new study in The Journal of the American Medical Association.

While the medical community continues to sort out the costs and benefits of prescribing HRT — and while safer forms of the hormones are presumably being developed — it’s a good idea to talk to your doctor about questions and concerns you may have about starting or stopping hormone therapy.

The new study uses data from the infamous Women’s Health Initiative (WHI) study which looked at HRT in postmenopausal women. The WHI was halted after about 5 years, because it was felt that the risks associated with the hormones outweighed their benefits. Some of these risks included more invasive forms of breast cancer and later cancer diagnoses, which meant that cancers were more often late-stage by the time they were discovered, and therefore more difficult to treat.

The current study, led by Rowan Chlebowski at UCLA, followed up with 12,800 women from the WHI study after the study it had been stopped. All women were postmenopausal and between the ages of 50 and 79. The researchers tracked the women’s incidence of breast cancer in the 11 years since the WHI study began and looked at how many of the women died over this period.

Chlebowski and his team found that women on HRT (again, estrogen plus progestin) were 25% more likely to develop an invasive form of breast cancer than women not taking hormones. They were also 78% more likely to have a cancer that metastasized (spread to the lymph nodes). Women on HRT were twice as likely to die from breast cancer as women who never took hormones, and they were more likely to die from any cause after a breast cancer diagnosis.

The use of HRT dropped after the WHI study was stopped in 2005. Still, as the authors point out, millions of women continue use of the therapy to combat the effects of menopause, which can be severe in some cases. While the medical community continues to sort out the costs and benefits of prescribing HRT — and while safer forms of the hormones are presumably being developed — it’s a good idea to talk to your doctor about questions and concerns you may have about starting or stopping hormone therapy.

The study was published in the October 20, 2010 online issue of The Journal of the American Medical Association.