e14607 Background: Both 5-FU and raltitrexed are thymidylate synthase inhibitors, but the latter has a toxicity profile that is distinct from 5-FU. Therefore, it is commonly used as an alternative to 5-FU in the treatment of colorectal cancer patients who have a history of cardiac problems or prior 5-FU cardiotoxicity. To date, the population-based risk of cardiac effects from raltitrexed is uncertain. Our aim was to characterize the patterns of treatment and outcomes of patients receiving raltitrexed-based chemotherapy. Methods: We conducted a retrospective study of all patients diagnosed with colorectal cancer from 1988 to 2012, evaluated at 1 of 5 regional cancer centers in British Columbia, Canada and treated with raltitrexed at any point during their disease. At the institutions in our province, raltitrexed use is limited to those in whom 5-FU is contraindicated. Using chi-squared tests and logistic regression analyses, we evaluated the associations between use of raltitrexed and various cardiovascular events, such as angina, myocardial infarction, hypertension and arrhythmias, as well as other toxicity outcomes, including nausea, vomiting and diarrhea. Results: A total of 186 patients were included: median age was 63 years (IQR 55-70), 97 (52%) were men, and 21 (11%) experienced at least one cardiovascular outcome. Only 4 (2%) patients had a documented cardiac history prior to receipt of any systemic therapy. Among the 21 cases of cardiovascular events, 10 reported angina, 1 suffered a myocardial infarction, 6 had hypertension, and 6 experienced arrhythmias. A significant number of patients also presented with other general toxicities: 25 (13%) reported fever, 11 (6%) suffered mucositis, 75 (40%) had nausea, and 51 (27%) experienced diarrhea. On regression analyses, patients with a previous history of coronary artery disease had a higher risk of cardiovascular events than those without (50 vs 11%, p=0.01). Exposure to 5-FU before raltitrexed did not increase cardiovascular outcomes (p=0.81). Conclusions: Raltitrexed is associated with a low risk of cardiovascular events, but its use should be monitored closely in those with prior coronary artery disease.