Abstract P1-05-11: The timing of BRCA1/2 germline testing and patient’s decision toward the risk-reducing mastectomy in breast cancer

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Abstract Background: BRCA1 and BRCA2 pathogenic variants significantly increase the risk of breast cancer. Risk-reducing mastectomy (RRM) is an option for these patients, offering substantial risk reduction. However, the decision to undergo RRM is complex and influenced by various factors. This study aims to analyze factors influencing RRM decisions in BRCA mutation carriers, with a particular focus on how the timing of BRCA testing affects the choice to undergo RRM. Methods: We conducted a retrospective analysis of 499 breast cancer patients diagnosed with germline BRCA1/2 pathogenic variants at Seoul National University Hospital between 2005 and 2023. Exclusion criteria included patients with distant metastasis at the time of BRCA testing, those who underwent palliative surgery at initial diagnosis, patients who had already undergone contralateral total mastectomy at the time of BRCA testing, and those initially diagnosed with bilateral breast cancer. Result: Of the 499 patients, 172 (34.4%) underwent RRM. Among the 262 patients who underwent BRCA testing before their initial breast cancer surgeries, 197 patients were aware of their BRCA mutation status prior to surgery, while for 65 patients, their BRCA test results became available after surgery. RRM rates were significantly higher in patients who knew their BRCA status before surgery compared to those whose results became available after surgery. (65.0% vs. 18.5%, p <0.001). Moreover, only 13.5% of patients who underwent BRCA testing after primary surgery subsequently underwent RRM. In the subset of 68 patients diagnosed with contralateral breast cancer (CBC) during follow-up, RRM rates were higher among those aware of their BRCA status before surgery for CBC compared to those who learned results post-operatively (32.4%vs. 11.7%, p = 0.079). However, this difference was not statistically significant. The results of the multivariate analysis showed that the timing of BRCA genetic testing emerged as a significant factor influencing the decision for RRM. Patients who underwent testing before their initial surgery were 10.1 times more likely to undergo RRM compared to those tested after surgery (95% CI: 6.09-17.20). Additionally, BRCA1 mutation carriers were found to be 1.8 times more likely to undergo RRM than BRCA2 carriers (95% CI: 1.12-2.88). Additionally, patients who received neoadjuvant chemotherapy were 1.8 times more likely to undergo RRM compared to those who did not (95% CI: 1.07-2.84). In contrast, other factors including age at diagnosis, sex, family history of breast or ovarian cancer, personal history of ovarian cancer, and presence of bilateral breast cancer were not significantly associated with the decision to undergo RRM. Conclusion: The timing of BRCA testing significantly influences decisions on risk-reducing mastectomy (RRM). This finding underscores the importance of considering genetic testing timing in breast cancer management. Clinicians should take this into account when planning BRCA testing to optimize patient decision-making regarding risk-reduction strategies. Citation Format: Eunhye Kang, Hyerim Kang, Changhoon Lee, Min Jung Lee, Jinyoung Byeon, Ji-Jung Jung, Hong Kyu Kim, Han-Byoel Lee, Wonshik Han, Hyeong-Gon Moon. The timing of BRCA1/2 germline testing and patient’s decision toward the risk-reducing mastectomy in breast cancer [abstract]. In: Proceedings of the San Antonio Breast Cancer Symposium 2024; 2024 Dec 10-13; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2025;31(12 Suppl):Abstract nr P1-05-11.

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