During the 10 years after breast cancer diagnosis, about five percent of women develop cancer in the opposite breast, known as contralateral breast cancer. According to a new study in JAMA Oncology, estrogen blocking drugs can decrease the risk of contralateral breast cancer, especially among women whose breast cancer was estrogen receptor positive.
Researchers from the National Cancer Institute reviewed the records of more than 7,500 women diagnosed with invasive breast cancer from 1990 to 2008. They followed the women through 2011 to see which patients developed breast cancer in the opposite breast. The researchers also recorded who took tamoxifen or aromatase inhibitors, two types of medications that block estrogen.
The researchers found that women who took these drugs for a longer period of time had a lower risk of contralateral breast cancer.