Abstract Background: The relationship between cirrhosis and breast cancer treatment and outcomes has not been specifically explored. We evaluated the association between cirrhosis and surgical outcomes in female patients with breast cancer. Methods: We performed a retrospective cohort study of female patients undergoing surgery for breast cancer between 2007-2018 using health administrative data from Ontario, Canada. Breast cancer surgeries were captured using Canadian Classification of Health Intervention codes. Patients with cirrhosis were identified using validated coding definitions. Overall and cancer-specific survival from time of surgery to December 2021 was compared between patients with and without cirrhosis using Kaplan-Meier survival analysis. Modified Poisson regression, chi-square and ANOVA were used to assess the association between cirrhosis and 90-day post-operative mortality, post-operative complications, length of hospital stay, intensive care unit (ICU) admission, and post-operative hepatic decompensation within 6 months. Results: A total of 83,880 females with breast cancer undergoing surgery were identified with 910 (1%) having cirrhosis. The median age at diagnosis was 65 (IQR 57-72) in patients with cirrhosis and 61 (IQR 51-71) in those without (p< 0.001). The most common etiology of cirrhosis was non-alcoholic fatty liver disease (n = 602, 66%) followed by alcohol-related (n =144, 16%) with n=27 (3%) having a history of decompensation within two years prior to surgery. Model for end stage liver disease score (MELD-Na) was available in 24% (n = 218), with a median score of 8 (IQR 6 – 11). Patients with cirrhosis had similar breast cancer stage at diagnosis as patients without cirrhosis (47% stage I, 38% stage 2, 11% stage 3, and 0.5% stage 4) with the most common type of surgical procedure being lumpectomy (71%) in both groups. Use of pre-operative chemotherapy was less common in patients with cirrhosis (5.9% vs 7.9%, p=0.026). Post-operative radiation and chemotherapy within 6-months after surgery was lower in patients with cirrhosis (56.8% vs 63.7%, p< 0.001 and 48.4% vs 52.2%, p=0.019, respectively). Patients with cirrhosis had higher 90-day post-operative mortality compared to those without (1.4% vs 0.3%, p < 0.001). After adjusting for age, income quintile, and breast cancer surgery, cirrhosis was independently associated with 90-day post-operative mortality (RR, 4.1; 95% CI 2.4-6.8). Patients with cirrhosis had a higher prevalence of incision complications (6.4% vs 4.6%, p= 0.007) and blood transfusions (2.9% vs 1.1%, p < 0.001), but similar rates of surgical site infections (6.4% vs 5.3%, p=0.138) and venous thromboembolism (0.3% vs 0.5%, p=0.5). Re-operation was slightly higher in patients without cirrhosis (3.2% vs 4.6%, p=0.05). Length of hospital stay was 2 days in patients with cirrhosis and 1.3 days for patients without (p < 0.001); ICU admission was more likely in patients with cirrhosis (1.8% vs 0.9%, p=0.008); and 18 (2%) patients with cirrhosis developed post-operative hepatic decompensation within 6 months. Survival in patients with cirrhosis was lower than those without (5-year OS 77% vs 87%, p< 0.0001); stage 0/I (83% vs 94%, p< 0.05), stage II (75% vs 87%, p< 0.05), stage III (62% vs 73%, p< 0.05), stage IV (40% vs 40%). Cancer-specific survival was also lower in patients with cirrhosis (5-year CSS 88% vs 91%, p=0.017). Conclusion: This large population-based study demonstrates that, compared to patients without cirrhosis, patients with cirrhosis are older with similar stage at diagnosis, but are somewhat less likely to receive adjuvant therapies. While they have slightly higher risks of certain post-operative complications and lower overall and cancer-specific survival, their outcomes remain favourable and should be considered for curative-intent therapies. Citation Format: Manisha Jogendran, Jennifer Flemming, Maya Djerboua, Shaila Merchant, Sean Bennett. Cirrhosis is associated with worse post-operative survival among patients with breast cancer: a population-based study [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-18-01.