Real-world use of biologics and its association with outcomes in RAS wild-type (WT) leftsided metastatic colorectal cancer (mCRC) in Canada.

56 Background: The use of biologics in combination with chemotherapy early in the course of treatment in mCRC improves outcomes, but whether this approach is uniformly adopted in clinical practice is unclear. This study aims to describe biomarker testing, treatment patterns, and survival of RAS WT, left-sided mCRC patients in a real-world population. Methods: We performed deterministic linkages with population-based data sources, including the cancer registry, pharmacy data, electronic medical records, and vital statistics to identify all patients who were diagnosed with RAS WT, left-sided mCRC, and treated with first-line (1L) combination systemic therapy from 2014 to 2019 in Alberta, Canada. Patients were followed until December 31, 2020. Results: Of 2,721 patients with left-sided mCRC, 1,375 were referred and received systemic therapy, 977 underwent RAS testing prior to or within 30 days of initiating 1L treatment, and 420 were found to be RAS WT. Among them, 320 were treated with 1L combination systemic therapy: FOLFOX/CAPOX/FOLFIRI (n=204), panitumumab (pani) with doublet chemotherapy (n=64), or bevacizumab (bev) with doublet chemotherapy (n=52). The interval from diagnosis to RAS test results was 38 (IQR 24-61) days. Only 207 (65%) and 125 (39%) of the 320 1L-treated patients reached 2L and 3L therapy, respectively. Median overall survival based on the different 1L regimens are summarized. Conclusions: Many real-world patients with mCRC were not exposed to biologics as part of their front-line treatment. There is a need to enhance RAS testing in 1L as 29% of patients were not tested, despite recommendations from guidelines. Because attrition across lines of therapy is high in mCRC, the opportunity to receive and benefit from biologics in later lines of therapy may be importantly reduced. [Table: see text]