BSBM-03 EXPLORING FACTORS ASSOCIATED WITH BRAIN METASTASES DEVELOPMENT AMONG BREAST CANCER PATIENTS RECEIVING NEOADJUVANT CHEMOTHERAPY

Abstract BACKGROUND One strategy to reduce the burden of brain metastases (BrM) among patients with breast cancer (BC) is to evaluate prevention strategies among those with early-stage disease. METHODS A retrospective study of patients treated with neo-adjuvant chemotherapy (NAC) for BC at the Sunnybrook Odette Cancer Centre from 2008-2019. Descriptive statistics were used to summarize patient and treatment characteristics. Cumulative Incidence Function (CIF) curves for recurrence were generated and Fine-Gray regression was used to model the effect of covariates. Both univariate analyses and multivariable modelling using backward selection with Akaike information criterion were used. Statistical significance was defined as p<.05. RESULTS Among 469 patients, 25 developed BrM with a median follow-up of 43.4 months (IQR 21.9-73.4). Most patients (n=191, 40.7%) had HR+/HER-, 177 (37.7%) had HER2+ and 98 (20.9%) had triple negative BC. Following NAC, 129 patients (27.5%) achieved a pathologic complete response (pCR). In a Fine-Gray model accounting for competing risk of death, residual node positive disease [HR 2.68, (95%CI 1.13-6.34), p=0.025)], inflammatory BC [HR 5.3 (95% CI 2.23-12.58), p<0.001], presence of lymphovascular invasion [HR 2.53 (95%CI 1.15–5.55, p=0.021] and lack of pCR [HR 4.55 (95%CI 1.04–20.0), p=0.044] were associated with a higher risk of BrM. Among patients with node-negative status post NAC, the cumulative incidence of BrM was 3.5% (95%CI 1.5–6.8%); the cumulative incidence of BrM was 18.6% and 26.4% among those with residual node positive HER2+ or triple negative BC (n=73) or those with residual node positive HR+/HER2- (n=140) disease, respectively. Only inflammatory BC was independently associated with development of BrM; among 44 patients with inflammatory BC the cumulative incidence of BrM was 24.5% (95%CI 11.2–40.5%). CONCLUSIONS Patients with inflammatory BC or residual nodal disease post NAC have a high incidence of BrM and may benefit from trials evaluating BrM prevention strategies.