Breast cancer patients with dense breasts are twice as likely to develop cancer in the other breast, according to research from the University of Texas MD Anderson Cancer Center.
The study, “Mammographic breast density is associated with the development of contralateral breast cancer,” is one of the first to describe the association between breast density and risk of cancer in the non-cancerous breast. It was published in the journal Cancer.
Understanding patients’ risk of developing cancer in their other breast — or contralateral breast cancer — is critical to their making informed decisions about their treatment. Women at high risk should consider bilateral mastectomy, or removal of both breasts.
Isabelle Bedrosian, MD, said the 10-year risk for contralateral breast cancer is as low as 2 percent in certain patients, but is as high as 40 percent in other patient subsets. The wide range depends on the risk factors affecting each patient, she explained.
“We know there are a number of well-established influences for developing both primary and secondary breast cancers, such as BRCA mutations, family history, and the tumor’s estrogen receptor status,” Bedrosian, an associate professor of breast surgical oncology at the Anderson center, said in a news release. “We also know density is a risk factor for the development of primary breast cancer. However, no one has closely looked at it as a risk factor for developing contralateral disease.”
The team conducted a retrospective, case-control study that covered 680 patients with stage 1 to 3 breast cancer who were treated at the Anderson center between 1997 and 2012. Women with BRCA mutations were excluded from the analysis because they are at higher risk for contralateral breast cancer.
Researchers divided the patients into 229 who had developed contralateral breast cancer and 451 who had not. The non-contralateral patients were the controls. Those with contralateral breast cancer and the controls were matched on age, years after diagnosis, hormone receptor status, and other factors.
Researchers assessed which patients in each group had dense breasts, based on mammogram readings and categorizations from the American College of Radiology. Dense breasts are those with a high level of breast and connective tissue, compared with fat.
Only 51.7 percent of the controls had dense breasts at diagnosis, but the percentage was 60.7 percent among those who developed contralateral breast cancer.
After adjusting for other breast cancer risk factors, the researchers concluded that patients with dense breasts were two times more likely to develop contralateral breast cancer than women with non-dense breasts.
“Our findings have valuable implications for both newly diagnosed patients with dense breasts and for breast cancer survivors as we manage their long-term risk of a secondary diagnosis,” said Carlos Barcenas, MD, assistant professor of breast medical oncology at the Anderson center and the study’s corresponding author. “Our future goal is to develop a risk model incorporating breast density to best assess a breast cancer survivor’s risk of developing CBC.”