The efficacy of anti-EGFR therapy across different lines of treatment in <i>RAS</i> wild-type left-sided metastatic colorectal cancer.

86 Background: Anti-epidermal growth factor receptor monoclonal antibodies (anti-EGFR mAbs) are recommended as a first-line treatment in RAS wild-type (RASwt ) left-sided metastatic colorectal cancer (mCRC). However, the efficacy of these therapies across different treatment lines remains unclear. This study aims to evaluate the efficacy of anti-EGFR mAb across first, second, third, and later-line treatments. Methods: We conducted a retrospective analysis of patients diagnosed with RASwt mCRC who received anti-EGFR mAb in all treatment lines at Siriraj Hospital between 2008 and 2023. The impact of anti-EGFR mAb treatment line on progression-free survival (PFS) and overall survival (OS) was determined using the Kaplan-Meier method and compared with the log-rank test. Results: Of the 350 patients with RASwt mCRC receiving anti-EGFR mAb, 33% (115 of 350) were treated in the first-line, while 16%, 45% and 6% were treated in the second-, third- and later-line settings, respectively. Eighty-six percent of patients had left-sided tumors, and anti-vascular growth factors were used in 34% of patients. The median follow-up time was 30.4 months (mo). Among patients with left-sided tumors, those receiving first-line anti-EGFR mAb treatment exhibited a significantly longer mPFS (11.9 mo, 95% CI 7.4-16.3, p&lt;0.001). The mPFS in the second-, third- and later-line settings were 6.1 mo (95% CI 4.6-7.5), 4.9 mo (95% CI 3.8-6.0), and 5.1 mo (95% CI 2.3-7.9), respectively. There were no significant differences in terms of OS across treatment lines (p=0.27). Conclusions: Although first-line treatment with anti-EGFR mAb had the longest mPFS in left-sided mCRC, OS did not significantly differ among treatment lines. Therefore, anti-EGFR mAb can be incorporated as a part of therapy at any line of treatment.