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Oestradiol Alone Does Not Increase Breast Cancer Risk: Presented at SABCS

By Charlene Laino

SAN ANTONIO, TX -- December 16, 2002 -- Hormone replacement therapy containing progestins significantly elevates breast cancer risk, but preparations containing oestradiol alone do not, a large Swedish observational study suggests.

Teasing out the component of hormone replacement therapy (HRT) that increases breast cancer risk has taken on added urgency since the HRT arm of the prospective U.S. Women's Health Initiative was abruptly halted in July 2002. The trial showed that the risks of HRT, including breast cancer, were found to outweigh its benefits in a large cohort of women.

The new study found that a 50-year-old woman who took a progestin-containing preparation for at least 48 months had a 10-year cumulative risk of breast cancer of seven percent. For a 50-year-old woman who used an oestrogen-only-containing preparation or never used HRT, the corresponding figures were three percent and two percent, respectively.

Hakan Olsson, MD, of the Department of Oncology at University Hospital, Lund, Sweden, presented the results here on December 13^th at the 25^th Annual Meeting of the San Antonio Breast Cancer Symposium.

The population-based cohort comprised 29,508 Swedish women aged 25 to 65 years and in good health when interviewed between 1990 and 1992.

By December 2001, 556 women had developed breast cancer. About 3,663 women in the entire cohort had used HRT at some point in their lives. A Cox regression model was used to analyse time to breast cancer development in relation to duration and type of HRT use, adjusting for known risk factors.

Compared with non-users, women who had used progestin-containing HRT for less than four years were 80 percent more likely to develop breast cancer. Women who used such preparations for four or more years had three times the risk of non-users.

In contrast, women who took oestradiol-only preparations for less than four years were 20 percent less likely to develop breast cancer than nonusers. And those who used such preparations for four or more years had only a 20 percent increased risk compared with nonusers.

The findings point to the need to develop new treatments for postmenopausal women, Dr. Olsson said. Among agents that are worthy of further study, he said, are the steroid tibolone and oestrogens in combination with low-dose progestin.

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