Breast density and the risk of contralateral breast cancer

This study investigated whether a high proportion of dense breast tissue is associated with an increased risk of developing contralateral breast cancer (CBC, cancer in the other breast). This study determined that those with dense breasts at the time of original diagnosis were significantly more likely to develop CBC than those without.

Women with a high proportion of dense breast tissue are known to have a significantly increased risk of developing primary breast cancer. CBC is a secondary cancer characterized by the presence of a tumor in the opposite breast which is detected at least 6 months after the original diagnosis of breast cancer. It is the most common form of secondary cancer found in women with breast cancer. Hormone receptor-positive status (tumors dependent on the hormones estrogen or progesterone for growth) and obesity are known to increase the risk of developing CBC. It is not clear whether dense breast tissue also increases the risk of CBC.

This study included 680 female patients with stage I – stage III breast cancer. The records and mammographic images from the time of initial diagnosis were examined. 229 women who developed CBC were compared to 451 who did not.  Of the women who developed CBC, 60.7% had dense breast tissue based on their mammograms.

Patients with a higher proportion of dense breast tissue were 80% more likely to develop CBC than those without. Those who developed CBC were also slightly less to have been treated with hormone therapy, chemotherapy or radiotherapy during their care. A high body mass index (measure of body fat that takes height and weight into account) at time of diagnosis was also associated with an increased risk of CBC.

This study concluded that women with dense breasts at the time of breast cancer diagnosis are significantly more likely to develop CBC than those without.

This study is limited by the small sample size and reliance on patient records. This meant that significant variation existed in the patient populations, length of follow up and the working definition of CBC.

Discuss the potential risk of CBC with your doctor.