Efficacy and tolerability of cetuximab 750 mg/m2 every three weeks in metastatic colorectal cancer

Earlier studies that established weekly dosing of cetuximab did not reach a maximum-tolerated dose. Subsequent pharmacokinetic studies showed equal efficacy and toxicity for the dose of 500 mg/m² every-2-weeks in combination with chemotherapy. This study aims to report the tolerability and efficacy of cetuximab at a dose of 750 mg/m² every-3-week (q3w) in combination with chemotherapy in metastatic colo-rectal cancer (mCRC).

This is a retrospective review. Data of patients with RAS wild-type (wt) mCRC treated with chemotherapy in combination with cetuximab at a dose of 750 mg/m2 q3w at two tertiary cancer centers were abstracted and analysed for efficacy and tolerability. Response assessment followed Response Evaluation Criteria in Solid Tumors (RECIST). Adverse effects reported based on Common Terminology Criteria for Adverse Events (CTCAE) version 5. Survival analysis was estimated by using the Kaplan-Meier estimator.

Eleven patients were identified. The median age was 58 years (range 28-69). All patients had BRAF wt. The primary site was left sided in ten patients and right sided in one. Eight patients (73%) had de-novo metastatic disease with the liver being involved in six patients (55%) at diagnosis. Cetuximab was given as first line in six patients, second line to three, and beyond second-line in two patients. The chemotherapy backbone was XELOX in ten patients, and irinotecan in one. The median relative dose intensity was 87%, 93%, and 99% for oxaliplatin, capecitabine, and cetuximab, respectively. Observed toxicity included grade (G) 2 infusion reaction in one patient, G2 acneiform rash in seven patients, and G2, and 4 diarrhea in two patients. All patients had hypomagnesemia G1. The median duration of follow-up was eight months (range 2-75). Response evaluation showed partial response in seven patients (64%), stable disease in one (9%), and disease progression in three patients (27%). The median progression-free survival was 8 months (95% CI, 2.56-13.43).

Cetuximab at a dose of 750 mg/m² q3w in combination with chemotherapy had manageable toxicity and encouraging efficacy in patients with RAS-wt mCRC. The small sample size is a limitation of the above conclusion. A prospective evaluation of the above regimen is warranted.

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