Tamoxifen reduced breast density, leading to reduced breast cancer risk

San Antonio Breast Cancer Symposium

SAN ANTONIO — Two in five women assigned to tamoxifen experienced a reduction of at least 10% in breast density, and in turn saw their risk for cancer drop by nearly two-thirds, according to the results of the IBIS-1 trial.

Jack Cuzick, PhD, head of the Cancer Research U.K. Center for Epidemiology, Mathematics and Statistics in London, discussed the results at a press briefing Friday during the San Antonio Breast Cancer Symposium.

“This is the first time that we’ve really found a biomarker that predicts a response to these preventive treatments, so it raises a lot of questions as to how broadly and how widely this can be used,” he said.

Researchers at multiple sites in the United Kingdom evaluated mammograms from 946 healthy controls and 126 women with breast cancer. Of these women, 48 with breast cancer and 456 controls had been randomly assigned to the tamoxifen arm. Evaluating these women 12 to 18 months after baseline, the researchers found that 46% of those assigned to the drug decreased breast density by 10% or more.

“The women who had a 10% or more loss of breast density — and that was a substantial proportion of women in the tamoxifen arm, over 40% — had an OR of 0.37, so a 63%, almost two-thirds, reduction in all breast cancers in that subgroup,” Cuzick said.

He added that tamoxifen had no preventive effect for women who did not see their breast density decrease by at least 10%. – by Jason Harris

Cuzick et al have shown mammographic density to be adaptable, meaning than an anti-estrogen can lower that density and — the most important aspect of the study — that was associated with reduced breast cancer incidence. The modulation of this marker, mammographic density, is predicting in part who is going to benefit from the cancer preventive effect of anti-estrogens. If you do not lower the density, the researchers found those people had no cancer preventive benefit from tamoxifen. That is a big help. Without this new advance, those people would normally be recommended to tamoxifen and be at risk for side effects when they were getting no benefit. This helps remove those women who do not benefit from tamoxifen from the risk of side effects.

– Powel H. Brown, MD, PhD

Dan L. Duncan Professor of Molecular and Cellular Biology, Baylor College of Medicine

For more information:

Cuzick J. #61. Presented at: the 31st Annual CTRC-AACR San Antonio Breast Cancer Symposium; Dec. 10-14, 2008; San Antonio.