Therapeutic radiation for breast cancer in BRCA mutation carriers and contralateral breast cancer (CBC) risk

Abstract

611 Background: BRCA mutation carriers diagnosed with breast cancer are at high risk for contralateral second primary breast cancers. Mutations in BRCA1 and BRCA2 lead to defects in DNA repair. Radiation treatment for breast cancer is felt to increase risk of CBC, but the interaction between BRCA status and local radiation therapy with respect to their effects on CBC is unclear. Methods: Through an IRB approved database registry at the Cleveland Clinic, breast cancer patients tested for BRCA1 and BRCA2 mutations were identified and evaluated for CBC events and radiation treatment history. Patients with inadequate clinical follow-up, those with bilateral synchronous breast cancer and those undergoing bilateral mastectomy within one year of the original breast cancer diagnosis were excluded from the analysis. Chi-square test was used to compare CBC rates with or without prior radiation separately in patients testing positive and those testing negative for BRCA mutations. Results: Of 115 identified breast cancer patients tested for BRCA mutations, 57 met the inclusion criteria. Twenty-one carried BRCA1 or BRCA2 mutations and 36 tested negative for these mutations. Median follow-up for the two groups was 69.5 months (92 months in BRCA positive group and 51.5 months in BRCA negative group). Median age at diagnosis was 45 years (41 years in BRCA positive group and 48.5 in BRCA negative group). Among the 21 carriers, 9 patients (43%) developed CBC while only 3 of 36 patients (8%) testing negative for BRCA mutations developed CBC. Thirteen of 21 mutation carriers (62%) had received radiation treatment for the original cancer: CBC occurred in 3 of 13 (23%) radiated patients and 6 of 8 (75%) patients who had not received radiation (p= 0.02). Among 36 patients with negative BRCA testing, 30 (83%) had received radiation: CBC occurred in 3 of 30 (10%) mutation negative patients who had received prior radiation and in 0 of the 6 patients who had not received radiation (p = 0.42). Conclusions: CBC incidence was higher among BRCA mutation carriers than a control group suspected of having hereditary breast cancer but testing negative for these mutations. The use of radiation in the presence of a BRCA mutation, however, does not appear to further increase the risk for CBC. No significant financial relationships to disclose.