Background The Sars Cov-2 pandemic and the national lockdowns disrupted healthcare systems in 2020. We assessed the impact on care pathways and clinical outcomes for new breast cancers (BCs) in Paris area. Methods We performed a retrospective multicenter cohort study on the data warehouse of Greater Paris University Hospitals (APHP). We identified pts newly referred with BC between Jan 2019, and Dec 2020. We assessed the delays of care management, the initial tumor stage from pathology and baseline PET/CT and CT-scan reports, and the trt categories: breast surgery, exclusive systemic therapy, exclusive radiation therapy, or exclusive best supportive care (BSC). We calculated pts’ 1-year overall survival (OS) and compared indicators for 2019 and 2020. Results In 2019 and 2020, 2,303 and 2,258 patients were newly referred with a BC diag among whom 2,055 and 1,988 female patients underwent a BC treatment, respectively. During the 1st and the 2nd lockdowns, the number of BC diag varied by -18% and by +23% compared to the same periods of 2019. Between 2019 and 2020, the rate of de novo metastatic disease (respectively 15% and 15%, p=0.95) did not differ, neither did the pTNM and the ypTNM distributions (p=0.37 and p=0.31). The time from 1st multidisciplinary meeting to trt did not differ (p=0.23). Pts’ access to reconstructive surgery (15% and 17%, p=0.08) and distribution across trt categories did not vary: tumor resection (73% and 72%), exclusive systemic trt (13% and 14%), exclusive radiation trt (9% and 9%), and exclusive BSC (5% and 5%) (p=0.8), respectively. Age-based subgroup analyses yielded to similar results (p=0,95). The rate of neoadjuvant trt for resected pts was lower in 2019 (16%) compared to 2020 (20%) (p=0.02), especially in patients aged < 50 years (15% vs 21%, p=0,01), respectively. The 1-year OS rates in 2019 vs. 2020 were 99.3% vs. 98.9% (HR=0.96; 95% CI, 0.77-1.2), 72.6% vs. 76.6% (HR=1.28; 95% CI, 0.95-1.72), 96.6% vs. 97.8% (HR=1.09; 95% CI, 0.61-1.94), and 15.5% vs. 15.1% (HR=0.99; 95% CI, 0.72-1.37), in the trt groups, respectively. Conclusions Despite an initial decrease in new BCs, we did not observe any tumor stage shift, and OS did not vary significantly during Sars-Cov-2.