Risk-reducing surgeries for breast cancer in Brazilian patients undergoing multigene germline panel: impact of results on decision making.

Purpose: To assess the behavior change of high-risk breast cancer patients regarding the intention to undergo risk-reducing mastectomies (RRM) before and after genetic testing results and to identify the main influencing factors in decision-making.

Methods: Prospective cohort study conducted between November 2021 and October 2022 with women under follow-up at the high-risk outpatient clinic of the State University of Campinas (UNICAMP). Patients were referred for genetic testing, followed by counseling according to the test result.

Results: A total of 373 women were included. In the pre-genetic testing analysis, 54.1% of patients intended to undergo RRMs. After testing, 42.2% opted for the procedure. Behavior change occurred in 26.2%, mainly from "yes" to "no/don't know" (72,6%) (p < 0.001). The genetic test result was positive (LPV or PV) in 29.7% of patients. Among the 90 patients with positive results, 62 (68.9%) agreed to RRM, while 22 (24.4%) remained unwilling to accept RRM, regardless of the positive test. Significant influencing factors for behavior change pre- and post-genetic testing (in favor of surgery) in multivariate analysis were: positive genetic test result (OR 2.94, p < 0.001), personal cancer history (OR 2.7, p = 0.008), and ages between 40 and 49 years (OR 2.07, p = 0.008) and ≥ 50 years (OR 3.47, p < 0.001).

Conclusion: In a Brazilian population at high-risk for breast cancer and users of the public health system, it was observed that most desired RRM, however, when genetic testing and counseling were performed, behavior change was observed, especially when the result was positive.