A radiologist examines breast X-rays after a cancer prevention checkup. (Jean-Paul Pelissier/Reuters)

Women who received hormone replacement therapy were more likely to have advanced breast cancers and more likely to die from the disease, according to a follow-up study published Tuesday.

Researchers looked at 11 years of data from the Women's Health Initiative, which followed more than 12,000 post-menopausal women aged 50 to 79 at 40 clinical centres in the U.S.

The study is a follow-up to research published eight years ago that indicated the benefits of hormone replacement therapy in relieving menopausal symptoms such as hot flashes were outweighed by the risks of breast cancer, heart disease and stroke.

The follow-up study, published in the Journal of the American Medical Association, looked at data on breast cancer mortality. It found that women in the combined hormone replacement therapy group (HRT with estrogen plus progestin) were twice as likely to die of breast cancer as were women in the control group — 2.6 versus 1.3 deaths per 10,000 women per year.

The researchers found that HRT increased the incidence of invasive breast cancer, and a "significantly larger" proportion of women in the combined HRT group had breast cancers that had spread to lymph nodes.

HRT 'interfered with cancer detection'

"Combined hormone therapy increased breast cancer risk and interfered with breast cancer detection, leading to cancers being diagnosed at more advanced stages," said the authors, who are from the Los Angeles Biomedical Research Institute at Harbour-UCLA Medical Centre.

An accompanying editorial in the medical journal suggests that the "available data dictate caution in the current approach to use of hormone therapy, particularly because one of the lessons from the [Women's Health Initiative] is that physicians are ill-equipped to anticipate the effect of hormone therapy on long-term health."

After the initial results from the WHI trial were released in 2002, the incidence of breast cancer fell substantially — a decline that was attributed to fewer women opting for HRT after the trial results were publicized.

"The adverse influence of estrogen plus progestin on breast cancer mortality suggests that a future reduction in breast cancer mortality in the United States may be anticipated as well," the researchers wrote.

Last month, a Canadian study confirmed international declines in new breast cancer cases among post-menopausal women when the use of hormone replacement therapy fell sharply.