Exploring Real-World Outcomes of First Line EGFR Inhibitor Use, Cetuximab Versus Panitumumab, in Patients with Left-Sided, RAS Wild-Type, Metastatic Colorectal Cancer.

Background: Epidermal growth factor receptor inhibitors (EGFRi), most commonly cetuximab and panitumumab, are first-line options for patients with left-sided, RAS wildtype (RASwt) metastatic colorectal cancer. Limited data is available comparing EGFRi outcomes.

Methods: Data for patients diagnosed January 2015 to October 2024 was reviewed from TRACC, a prospective, multi-site Australasian colorectal cancer registry. Patients with left-sided, RASwt disease treated with an EGFRi as first-line (1 L) therapy were identified. Survival outcomes were calculated using Kaplan-Meir methods.

Results: We identified 747 patients with RASwt, left-sided, metastatic colorectal cancer. Of these, 287 (38%) received 1 L therapy that included cetuximab (n = 210, 73%) or panitumumab (n = 77, 27%). A switch from one to the other agent occurred in seven patients, all due to skin toxicity, including six patients (7.8%) initially treated with panitumumab and 1 (0.5%) initially treated with cetuximab. After switching, median time on the second EGFRi agent was 212 days. For 242 patients treated with an EGFRi in combination with doublet chemotherapy, toxicity contributed to treatment cessation more often in patients treated with panitumumab (32% vs. 13%, P = .003). For the subset of patients treated with palliative intent (n = 156), median progression-free (P = .43) and overall survival (P = .98) were similar for both EGFRi.

Conclusion: In this real-world analysis, a switch from one EGFRi agent to the other in the presence of skin toxicity led to durable treatment benefit with the alternate EGFRi. For patients receiving first-line cetuximab or panitumumab in combination with doublet chemotherapy, toxicity-related treatment cessation rates differed between EGFRi agents. No differences were seen in survival outcomes.