Women with breast cancer before the age of 55 years old who carry an inherited mutation in the breast cancer susceptibility genes BRCA1 or BRCA2 are four times more likely to develop cancer in the contralateral breast to their initial tumor as compared to breast cancer patients without these genetic defects. These findings were made by Fred Hutchinson Cancer Research Center breast cancer epidemiologist Kathleen Malone, PhD.
Compared to non-carriers, breast cancer patients with a BRCA1 mutation had a 4.5-fold increased risk and those with a BRCA2 mutation had a 3.4-fold increased risk of a subsequent contralateral breast cancer, the researchers found. Carriers of either mutation who were diagnosed with breast cancer before age 55 faced an 18% cumulative probability of developing cancer in the opposite breast within 10 years as compared to a 5% cumulative probability among women who were mutation-free.
“For young women with breast cancer, our results reinforce the message that early-onset disease is much more likely to be associated with a BRCA mutation,” Malone, first author of the paper and a member of the Public Health Sciences Division at the Hutchinson Center, said in a news release.
While only about 5% of breast cancer patients across all age groups carry a BRCA mutation, the younger a woman is at the time of her first breast cancer diagnosis, the more likely she is to have such a mutation.
“In the youngest patients in our study – those with a first cancer diagnosed before age 35 – we found that 16% of those with one breast tumor and 54% of those who had developed two primary breast cancers carried a mutation,” Malone said.
Mutation frequencies were elevated also in women diagnosed with a first cancer between ages 34 years and 44 years; among those initially diagnosed with one breast tumor the mutation frequency was 6.3; those diagnosed with two primary breast cancers had a mutation rate of 22%.
This international, multicenter study, which was coordinated by Memorial Sloan Kettering Cancer Center, analyzed data from 705 women with contralateral breast cancer and a comparison group of 1,398 women with unilateral breast cancer. All of the women had been first diagnosed before the age of 55 years.
“While contralateral breast cancer risks in our study are quite substantial, it is worth noting that they are also 10% to 15% lower overall than in past studies in high-risk settings,” Malone said.
One reason for this, she said, is because this study is among the few to assess risk among substantial numbers of women without a positive family history of breast cancer.
“Getting these risk estimates right is important because of their role in clinical decision-making,” Malone said.