Background: Recent studies suggest that older women derive the same benefits from adjuvant systemic chemotherapy (AST) as younger women. In older women, the ability to successfully complete chemotherapy may be complicated by other health conditions and performance status. This study examines the frequency of inability to complete planned AST and factors associated with difficulty administering AST in older women. Methods: We performed a retrospective analysis of breast cancer patients (age≥65) who received adjuvant/neoadjuvant chemotherapy at Roswell Park Cancer Institute from 9/1997 to 1/2010. Endpoints considered collectively as “difficulty “ in delivering AST were delay in treatment, hospitalization, dose reduction and discontinuation of AST. Factors defined a priori that could affect these outcomes were creatinine clearance (CCr), obesity (BMI ≥30), cardiac disease, hypertension, psychiatric disorders, diabetes, cerebrovascular disease, previous malignancy, COPD/asthma, Charlson comorbidity index, and use of anthracycline-based chemotherapy. The Pearson chi-squared test was used to identify the significant categorical factors associated with each of the five binary responses indicating difficulty administering AST. Logistic regression was used to obtain crude and adjusted odds ratios to further examine the relationships. Kaplan-Meier methods were used to estimate survival distributions, progression free and overall survival. The log-rank test was used for comparison between women experiencing difficulty with treatment and those with no difficulty with treatment. A 0.05 nominal significance level was used in all testing. Statistical analysis and plots were completed using SAS, version 9.2, statistical software (SAS Institute Inc., Cary, NC). Results: 193 women age 65 and over received AST (median age of 70 years - range 65-86). Median follow up was 40.9 months. 73% received anthracycline-based AST. Factors associated with difficulty, delay, dose reduction, hospitalization, or failure to complete planned AST are shown in the Table. Women who completed planned AST had better OS than those who did not complete AST (p=0.01). Women who completed therapy with difficulty had no difference in outcome compared to those without difficulty [DFS (p=0.07) and OS (p=0.18)]. Conclusions: Age, cardiac disease, diabetes, hypertension, CCr, obesity, CCI, and sum of comorbidity significantly impact the ability to deliver and complete AST in older women with BC. Completing planned chemotherapy is associated with improved survival. Figures available in online version. Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P5-13-08.