Tamoxifen is often administered to women after surgery for breast cancer in the hope it will diminish the chance of recurrence but, other than the test of time, there has been little opportunity to know if the drug therapy is actually working.  Researchers from the United Kingdom (UK) announced  at the 31st Annual San Antonio (Texas) Breast Cancer Symposium that breast density may be a viable marker for success.

Jack Cuzick, PhD, from London’s Cancer Research UK Centre for Epidemiology, Mathematics and Statistics, says a reduction in breast density, as measured by mammography, is a promising indicator that the tamoxifen therapy is working and a patient’s risk of cancer recurrence is diminishing.  Follow-up studies are planned to further validate his research team’s findings.

Because other treatment options are available and still others are under investigation or development, Cuzick says knowing an individual patient’s response to tamoxifen allows her doctors to know when to continue tamoxifen therapy and when to try alternatives instead.  Evidence of success, as represented by reduced density in the breast, can be measured as early as 12 months after beginning treatment.

In a study that involved more than 7,000 women, Cuzick concluded tamoxifen does reduce the risk of recurrence by as much as 30% to 40% when the cancer is the estrogen receptor (ER) positive form.  This study, the International Breast Intervention Study I (IBIS-I), required baseline mammograms taken at the beginning of tamoxifen therapy and again at 18, 36, and 54 months.

Narrowing field for a second study, Cuzick’s research team recruited 120 IBIS-I breast cancer patients and 943 women free of cancer.  Breast density was monitored over time using mammography but other variables were considered as well, including body weight, family history, and hormone status.

All factors considered, Cuzick’s team concluded it was breast density that best predicted the success of tamoxifen treatment.  When breast density was reduced by at least 10%, the patient’s risk of developing breast cancer was reduced by 52%.  About 46% of the cancer patients in the study enjoyed this success.

Breast density was not reduced by 10% or more in the remaining 54% of study participants and their risk of developing subsequent cancer was diminished by only about 8%, a rate considered non-significant by the researchers.