Real-world analysis of the impact of timing of biomarker testing on first-line treatment choice in patients with metastatic colorectal cancer in British Columbia.

253 Background: The treatment landscape for metastatic colorectal cancer (mCRC) has evolved significantly, shifting from chemotherapy alone to more personalized approaches that include immune checkpoint inhibitors and targeted therapies. Treatment decisions in mCRC are driven by molecular characteristics, and current guidelines recommend a minimum standard of biomarker testing, such as mismatch repair (MMR) status, and RAS and BRAF mutations, at the time of metastatic disease diagnosis to guide treatment selection. This study aimed to assess the real-world implementation of biomarker testing in a contemporary cohort of mCRC patients in British Columbia (BC) and its impact on treatment decisions by medical oncologists. Methods: We conducted a retrospective chart review of patients who received first-line systemic therapy for mCRC in BC between January 2022 and December 2023. Patient demographics, tumour characteristics, and treatment details were obtained from the BC Cancer provincial pharmacy database. Medical oncology documentation and pathology reports were reviewed to determine the availability of biomarkers, including MMR status, and RAS and BRAF mutations (OncoPanel), at the time of initial medical oncology consultation, and to assess how these results influenced treatment plan. Results: To date, 71 eligible patients have been identified, with data collection ongoing. Of these, 82% had proficient MMR status, 17% had deficient MMR status, and 1% had incomplete data. RAS mutations were present in 55% of cases, while BRAF mutations were found in 21% (Table). At the time of the initial medical oncology consultation, MMR status was unavailable in 14 patients (20%), two of whom were later found to have deficient MMR status. OncoPanel results were unavailable for 63 patients (88%) at the time of the initial consultation, and in 16 of these cases (25%), the systemic therapy plan was modified once the results were received. Conclusions: Even in contemporary practice with publicly funded biomarker testing, the results for RAS and BRAF mutations were not available at the time of initial medical oncology consultation for most patients. Biomarker testing is an essential tool for guiding therapeutic decisions in mCRC. This subsequently led to treatment plan changes in one-quarter of cases after results were received. These findings highlight the importance of timely biomarker testing to ensure optimal and efficient treatment decision-making for all mCRC patients. Metastatic colorectal cancer biomarker testing. Proficient/WT Deficient/Mutated Incomplete MMR 58 12 1 RAS 29 39 3 BRAF 53 15 3