Risk Of Contralateral Breast Cancer Is Falling

Contralateral (opposite) breast cancer has declined annually in the USA by approximately 3% from the mid-1980s to 2006. Multiple explanations have been put forth, including the use of tamoxifen in the 1980s and 90s, aromatase inhibitors (anastrozole, letrozole, exemestane) in the early 2000s, a shift toward taxanes (Taxol and Taxotere) in chemotherapy regimens, and the use of trastuzumab (Herceptin) for HER2 positive cancers. Furthermore, contralateral prophylactic mastectomy usage has tripled to over 10% of those requiring unilateral mastectomy for cancer treatment. Researchers from the National Institute of Health recently published a study comparing the risk of contralateral breast cancer to breast cancer in the general population. They followed the risk of breast cancer developing in the opposite breast from the years 1992 to 2016.

In general, the study’s authors found that the relative risk of contralateral breast cancer is higher than the risk of developing breast cancer in the general population. It was notably higher for women who were initially diagnosed under the age of 40. They also found that it was somewhat higher in women having initial breast cancer that was estrogen receptor negative. They found that the risk, again compared to the general population, was slightly higher in women initially treated with chemotherapy than those treated with hormone therapy.

However, the most crucial part of the study came when the authors looked at the risk of developing contralateral cancer over time. The authors found that the risk of contralateral breast cancer decreased significantly over time when they compared periods from 1992-1997 to 2010-2015. This decrease in the risk of second breast cancers was noted over time regardless of the diagnosis age. Additionally, they noticed the same decline in women whose initial cancer was estrogen receptor positive or negative, including triple negative cancers. The authors noted a risk decrease in second cancers for women who had received chemotherapy and hormonal therapy. The researchers noticed the same trends over time, even when excluding patients who had prophylactic contralateral mastectomies.

Summary: This study from the National Institute of Health found that the risk of contralateral breast cancers is higher than that in the general population. However, most importantly, they found that this rate of developing second breast cancers has been continuously falling since 1992. They found that this reduction in the risk of contralateral breast cancers affected women whose first cancer was triple-negative and those whose first cancer was estrogen receptor-positive. Furthermore, they found a reduction in the risk of second cancers over time in those women who had chemotherapy and hormonal therapy. This reduction may be due to advances in chemotherapy and the more common use of aromatase inhibitor hormonal therapy.