Moderate radiation therapy on unaffected breast could prevent second breast cancers

A study conducted in mice suggests that survivors can dramatically reduce that risk of developing breast cancer in the other breast through treatment with moderate doses of radiation to the unaffected breast at the same time that they receive radiation therapy to their affected breast.

The treatment, if it works as well in humans as in mice, could prevent tens of thousands of second breast cancers, researchers at Columbia University Medical Center (CUMC) said.

"Over the past decades, we've had great success in treating breast cancer, and the 15-year survival rate is now 77 percent," study leader David J. Brenner, PhD, director of CUMC's Center for Radiological Research and the Higgins Professor of Radiation Biophysics, said.

"Unfortunately, breast cancer survivors have a several times higher risk of developing cancer in their other breast, compared with healthy women of the same age," he said.

Dr. Brenner added that while drugs such as tamoxifen and aromatase inhibitors can reduce the risk somewhat, at least for women with estrogen receptor-positive tumors, the long-term risks of a second breast cancer in the unaffected breast remain high.

Because of these risks, approximately 10 to 20 percent of breast cancer survivors in the U.S. undergo prophylactic mastectomy of their other breast.

The idea for prophylactic mammary irradiation (PMI) of the unaffected breast stems from an earlier study of standard whole-breast irradiation after lumpectomy.

In that study, Dr. Brenner found that radiation is highly effective at killing premalignant cells, not only in the quadrant of the breast where the primary tumor was located, but also in the other three quadrants, where premalignant cells are generally considered to be unrelated to the primary tumor.

"So, we thought, why can't we treat the other breast with a moderate dose of radiation and kill any premalignant cells that could lead to second cancers?" Dr. Brenner said.

The study is published in the online journal PLOS ONE.