Women with breast cancer who experience significant reductions in relative breast tissue density during tamoxifen treatment have their risk of death as a result of breast cancer cut in half, according to a study published online April 22 in the Journal of Clinical Oncology.

The results suggest monitoring breast tissue density with mammography could be an early way to assess response to the treatment used to prevent breast cancer relapse, according to Per Hall, MD, PhD, of the Karolinska Institutet in Stockholm, and colleagues.

While tamoxifen-induced breast density change has been shown to reflect breast cancer mortality in a preventive setting, it was not known whether it also would predict treatment response in women who had already developed cancer, explained the authors.

To that end, Hall and colleagues conducted an observational study of 974 postmenopausal breast cancer patients, 474 of whom received tamoxifen and 500 of whom did not. The authors used an automated thresholding method to measure mammographic density and express it as absolute dense area (DA). The women were followed for 15 years, during which 121 patients died from breast cancer.

Results showed those treated with tamoxifen who experienced density reduction of more than 20 percent between baseline and first follow-up mammogram had a 50 percent reduction in breast cancer mortality compared with women who had stable breast density. The non-tamoxifen group demonstrated no significant association between mammographic density change and survival.

Hall and colleagues noted the results did not change after controlling for predictors of mammographic density, tumor characteristics and breast cancer therapy.

“In contrast to treatment-associated DA, established prognostic indicators such as [estrogen receptor] status or tumor size typically have an effect on breast cancer–specific survival within the first 5 years, after which survival curves tend to converge. For women who survived at least until they received a follow-up mammogram after treatment, the prognostic value of DA assessed from the baseline and follow-up mammogram is informative up to 15 years past diagnosis, suggesting that  DA can serve as an early indicator of treatment response with long-term implications for breast cancer–specific survival,” wrote the authors.

They also pointed to the fact that since patients already undergo routine annual follow-up mammograms, no further exams are needed. Automatic algorithms to measure mammographic density could further improve cost-effectiveness.