Researchers associated with the Women’s Health Initiative (WHI) have confirmed that postmenopausal hormone therapy with combined estrogen plus progestin hormone replacement therapy (HRT) increases a woman’s risk of developing breast cancer. Researchers affiliated with the California Teachers Study also confirmed that postmenopausal women taking HRT tend to have less deadly breast cancers than women not on HRT. The results of both studies were presented at the 2008 San Antonio Breast Cancer Symposium.

Postmenopausal HRT effectively manages several common menopausal symptoms.  However, a large clinical trial conducted as part of the Women’s Health Initiative (WHI) raised concerns about the health risks of these therapies. In 2002, for example, it was reported that HRT increases the risk of breast cancer, heart disease, stroke, and blood clots. Women taking HRT had fewer fractures and were less likely to develop colorectal cancer, but for most women, these benefits were thought to be outweighed by the risks.

Researchers used updated information from the WHI clinical trial of estrogen plus progestin, as well as information from another component of the WHI (the WHI Observational Study) to further explore the relationship between estrogen plus progestin and risk of breast cancer.[1] 

• The results confirmed that users of estrogen plus progestin were more likely than nonusers to develop breast cancer. This increased risk declined markedly and fairly rapidly, however, once women stopped using hormones.

These analyses of the WHI data support the claim that the recent decreases in breast cancer incidence in the United States may be due to a reduction in the number of women using postmenopausal hormones. It also provides information to women and physicians about what happens to breast cancer risk after hormone cessation.

In a second presentation, researchers assessed the impact on breast cancer survival of hormone use prior to breast cancer diagnosis. Using information from the California Teachers Study, researchers examined breast cancer survival among 2,783 postmenopausal women with breast cancer.[2]

• After accounting for other factors that may influence breast cancer survival, women who used estrogen plus progestin before their breast cancer diagnosis were 47% less likely to die of breast cancer. There was a suggestion that estrogen alone may also decrease risk, but the effect was smaller and not statistically significant.

Comments: These two studies confirm previous observations about the association between use of HRT and breast cancer risk.  

References:

[1] Chlebowski RT, Kuller L, Anderson G et al. Breast cancer after stopping estrogen plus progestin in the Women’s Health Initiative. Presented at the San Antonio Breast Cancer Symposium. December 13, 2008. Abstract 64.

[2] Marshall SF, Chang E, Clarke CA et al. Hormone therapy use before diagnosis and breast cancer survival in the California Teachers Study. Presented at the San Antonio Breast Cancer Symposium. December 13, 2008. Abstract 65.