A new study published in the Journal of the National Cancer Institute demonstrates that tamoxifen treatment is associated with a reduction in mammographic breast density, an effect particularly pronounced in women aged 45 years and younger. Increased mammographic breast density has been identified as a risk factor for breast cancer.

Tamoxifen has been shown to lower the risk of breast cancer in high-risk women, but the drug's effect on breast density in healthy women has not been known. To investigate this, Jack Cuzick, Ph.D., of Cancer Research UK in London, and colleagues analyzed mammograms from 818 breast cancer-free women from the International Breast Cancer Intervention Study 1, a trial that tested tamoxifen's ability to prevent breast cancer in healthy women at high risk of the disease.

Treatment with tamoxifen was associated with reduced breast density, most of which occurred within the first 18 months of treatment. In women aged 45 years and younger, breast density was reduced by 13.4% on average compared with only 1.1% in women older than 55 years.

The researchers hypothesize that premenopausal women experienced a larger reduction because premenopausal estrogen levels are higher; therefore, the antiestrogenic effect of tamoxifen will be greater.

SOURCE:
Journal of the National Cancer Institute, April 21, 2004