Top Line: Do patients with germline BRCA 1 or 2 mutation have a higher risk of contralateral breast cancer after radiation for a primary breast cancer?
The Study: Patients with BRCA mutations are at increased risk of contralateral breast cancer (CBC). While some choose to have a risk-reducing mastectomy, others may not and instead opt for close surveillance. In this study, data from the International BRCA 1/2 Carrier Cohort Study (IBCCS) was used to identify 3602 breast cancer patients with germline BRCA 1 or 2 mutations. Of these, 64% received adjuvant radiation for their primary breast cancer and the rest did not. Patients who received radiation had higher stage, and they were more likely to receive chemo and endocrine therapy. The cumulative risk of CBC at 10 years was 10.4% after RT and 6.9% after no RT. A challenge in evaluating CBC risk was the competing event of contralateral mastectomy, which was done in 34% of RT patients and 43% of no RT patients. As we can see, the cumulative risk of CBC was relatively low compared to BRCA carriers in other large cohorts (CBC risk ~30%). With almost 10% more patients in the no RT group having risk reducing mastectomy, it may be difficult to account for changes in risk between groups over time. Overall though, the authors found that receipt of RT was associated with an increased risk of CBC. Over time, the risk seemed to peak around 5-6 years after treatment. Among subgroups, the effect was significant in BRCA2 carriers but not BRCA1 carriers. Age did not appear to influence the effect of RT on CBC risk with a similar hazard ratio for those younger versus older than 40. Another challenge in evaluating this study is that they didn’t actually have details about radiation therapy. So, they couldn’t directly associate radiation dose or exposure of the contralateral breast with CBC risk.
TBL: In this cohort of BRCA 1/2 mutation carriers with breast cancer, adjuvant radiation was associated with a slightly higher risk of contralateral breast cancer. Though it has limitations, the study should at least prompt us to pay careful attention to radiation dose to the contralateral breast in BRCA mutation carriers. | van Barele, JNCI
The Study: Patients with BRCA mutations are at increased risk of contralateral breast cancer (CBC). While some choose to have a risk-reducing mastectomy, others may not and instead opt for close surveillance. In this study, data from the International BRCA 1/2 Carrier Cohort Study (IBCCS) was used to identify 3602 breast cancer patients with germline BRCA 1 or 2 mutations. Of these, 64% received adjuvant radiation for their primary breast cancer and the rest did not. Patients who received radiation had higher stage, and they were more likely to receive chemo and endocrine therapy. The cumulative risk of CBC at 10 years was 10.4% after RT and 6.9% after no RT. A challenge in evaluating CBC risk was the competing event of contralateral mastectomy, which was done in 34% of RT patients and 43% of no RT patients. As we can see, the cumulative risk of CBC was relatively low compared to BRCA carriers in other large cohorts (CBC risk ~30%). With almost 10% more patients in the no RT group having risk reducing mastectomy, it may be difficult to account for changes in risk between groups over time. Overall though, the authors found that receipt of RT was associated with an increased risk of CBC. Over time, the risk seemed to peak around 5-6 years after treatment. Among subgroups, the effect was significant in BRCA2 carriers but not BRCA1 carriers. Age did not appear to influence the effect of RT on CBC risk with a similar hazard ratio for those younger versus older than 40. Another challenge in evaluating this study is that they didn’t actually have details about radiation therapy. So, they couldn’t directly associate radiation dose or exposure of the contralateral breast with CBC risk.
TBL: In this cohort of BRCA 1/2 mutation carriers with breast cancer, adjuvant radiation was associated with a slightly higher risk of contralateral breast cancer. Though it has limitations, the study should at least prompt us to pay careful attention to radiation dose to the contralateral breast in BRCA mutation carriers. | van Barele, JNCI