Real-world study of cetuximab used every other week versus weekly in US patients with metastatic colorectal cancer (mCRC).

Abstract

e15087 Background: After an initial dose of 400 mg/m², cetuximab (CET) at a dose of 250 mg/m² in combination with chemotherapy (CT) is approved for once-weekly (q1w) use in the treatment of RAS wild-type metastatic colorectal cancer (mCRC). However, off-label use of CET 500 mg/m2 administered every other week (q2w) has been observed in clinical practice. This study aimed to test the noninferiority of q2w vs q1w administration on overall survival (OS) using US claims data. Methods: Using IBM MarketScan, a large US insurance claims database, a cohort of patients with mCRC treated with CET + CT between 2010 and 2016 was identified and classified as q1w or q2w based on observed infusion patterns. The initial CET prescription was defined as the index date, and patient death was determined using a previously published algorithm. Confounding was accounted for using high-dimensional propensity scoring (hdPS) methodology with inverse probability of treatment weighting (IPTW). OS for both groups was compared using Cox proportional hazards regression. Confounders that remained imbalanced after hdPS with IPTW were added to the Cox model. The noninferiority of the q2w regimen was tested with a margin hazard ratio (HR) of 1.25 for q2w vs q1w. Results: 2,869 patients with mCRC exposed to CET were identified of which 1,865 (65.0%) and 1,004 (35.0%) were classified in the q1w and q2w groups, respectively. The mean age of patients was 60.1±11.7 years for q1w and 58.1±11.1 years for q2w. Most patients were male: 57.5% and 60.8% in q1w and q2w, respectively. Approximately 70% of patients in both groups had received prior treatment for mCRC. The most frequently used CT with CET was irinotecan based (64.5% in q1w and 76.5% in q2w). There were 1,628 deaths observed during follow-up (56.7%). After hdPS with IPTW adjustment, differences remained in associated CT (standardized difference <0.25). Crude HR for OS was 1.05 (95% CI, 0.94-1.18), and adjusted HR for OS was 1.04 (95% CI, 0.93-1.17). The inferiority hypothesis was rejected at p<0.001. Conclusions: In this large US claims database, when assessing OS, the q2w administration schedule was found to be noninferior to the q1w schedule in patients with mCRC.