It’s well known that women with dense breasts have a higher risk of primary breast cancer, but they also have a two-fold increased risk of developing cancer in the contralateral breast. This, according to new research from The University of Texas MD Anderson Center was published in the journal Cancer.
"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," Dr. Isabelle Bedrosian, study author and associate professor of breast surgical oncology at MD Anderson, said in a statement. "We also know density is a risk factor for the development of primary breast cancer.”
The approximate 10-year risk for women with breast cancer developing CBC is between 2 percent and 40 percent. The range is wide, largely because of the variability of risk factors across the patient population.
According to Bedrosian, no studies have looked closely at density as a risk factor for developing contralateral disease until now.
In the retrospective, case-controlled study, the researchers evaluated 680 stage I, II and III breast cancer patients treated at MD Anderson between 1997 and 2012. Patients with the BRCA mutation were excluded from the study because of they are known to have a high risk of CBC.
Women who were diagnosed with metachronous CBC in the opposite breast more than six months after the initial diagnosis were considered the ‘cases’ and those who didn’t develop CBC were the ‘controls.’ Of the selected patients, 229 were placed in the cases group and 451 in the control group.
The cases and controls were matched on a 1:2 ratio, based on a factors including age, year of diagnosis and hormone receptor status. The researchers categorized each patient’s breast density as dense or non-dense using the categorizations from the American College of Radiology.
In the cases group, 39.3 percent were classified as having non-dense breast tissue and 60.7 percent as having dense breast tissue. Among the controls, 48.3 percent had non-dense and 51.7 percent had dense breast tissue.
"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 Barcenas. "Our future goal is to develop a risk model incorporating breast density to best assess a breast cancer survivor's risk of developing CBC."
A major challenge in managing this patient population is trying to counsel them appropriately on their risk of developing CBC. The researchers are hoping to use the risk model to counsel patients on their personal risk and the options for treatment and surveillance if their risk if sufficiently high.
