Real-world use of anti-EGFR therapy in metastatic colorectal cancer.

3552 Background: Anti-EGFR therapies including cetuximab and panitumumab are recommended in frontline or later-line treatment regimens for left-sided metastatic colorectal cancer (mCRC) lacking mutations in RAS or BRAF. Here we report patterns of anti-EGFR therapy use in patients with mCRC diagnosed between 2013 and 2023. Methods: This study used the nationwide Flatiron Health electronic health record (EHR)-derived de-identified database, which contains patient-level data originating from approximately 280 cancer clinics in the United States (~800 sites of care).Adult patients diagnosed with mCRC from January 1, 2013 to April 28, 2023 who received at least 1 line of treatment were included. The percentage of patients who received anti-EGFR agents based on biomarker indication and primary tumor sidedness (PTS) was determined. PTS was assessed by ICD codes, with left-sided disease defined as tumors originating from the splenic flexure to the rectum. Univariate and multivariable analyses were performed to evaluate for factors associated with utilization of biomarker-directed anti-EGFR therapy. Results: A total of 25,937 patients were included in this analysis. Among these, 3,425 (13.2%) had a confirmed indication for anti-EGFR therapy, based on the presence of left-sided disease and documented KRAS, NRAS,and BRAFwildtype status (Cohort 1). In contrast, 15,015 (57.9%) patients had a documented RASor BRAF mutation and/or right-sided disease (Cohort 2). Anti-EGFR therapy was included in frontline treatment for 19.7% of patients in Cohort 1 versus 3.3% of patients in Cohort 2. Anti-EGFR therapy was included in any-line treatment for 56.6% of patients in Cohort 1 versus 12.1% of patients in Cohort 2. Patients in Cohort 1 were less likely to receive anti-EGFR therapy in any treatment line if they were ≥ 75 versus < 45 years old at diagnosis (odds ratio OR 0.72, p = 0.027), had a primary rectal versus colon cancer (OR 0.87, p = 0.045), or were diagnosed at a later timepoint. For instance, while 72.4% of Cohort 1 patients diagnosed between 2013-2015 received anti-EGFR therapy, only 63.9% (OR 0.68, p = 0.05), 59.5% (OR 0.57, p < 0.001), and 46.7% (OR 0.34, p < 0.001) of patients diagnosed between 2016-2017, 2018-2019, and 2020-2023 received anti-EGFR therapy, respectively. Patient sex, race, ethnicity, practice setting, socioeconomic index, and performance status were not associated with anti-EGFR therapy use. Conclusions: Based on results from the Flatiron Health database, use of anti-EGFR therapy is enriched among patients with biomarker-based indications for treatment. Notably, anti-EGFR therapy was employed in only 56.6% of patients with RAS and RAF wildtype, left-sided mCRC, with decreased use observed from 2013 to 2023.