Panitumumab versus cetuximab in combination with irinotecan in refractory metastatic colorectal cancer

There is evidence that adding cetuximab can overcome resistance to irinotecan, but a similar analysis with Panitumumab isn't readily available. This study evaluated the activity of each anti-EGFR plus irinotecan as a salvage third-line treatment for metastatic colorectal cancer.

This is a retrospective cohort of metastatic colorectal cancer patients who progressed to irinotecan monotherapy and were exposed to an anti-EGFR antibody as a third line of treatment. This study was conducted at a single cancer center in Brazil. The primary outcome was overall survival. The secondary outcomes were objective response rate, stratified by primary tumor sidedness, progression-free survival, and toxicity.

This analysis included 412 patients who had progressed on irinotecan and were KRAS wild-type. One hundred eighty-two received Irinotecan plus Cetuximab (I + C group) and 230 Irinotecan plus Panitumumab (I + P group). There was no significant difference in median overall survival between treatment groups (9.1 months [I + C] vs 10.1 months [I + P]; p = 0.76). There was also no difference in progression-free survival (3.63 months [I + C] vs 3.73 months [I + P]; p = 0.19) and objective response rate (23.0 % [I + C] vs 22.3 % [I + P]; p = 0.97). Patients with right-sided tumors had worse overall survival than left-sided (6.2 months vs 10.1 months; p = 0.003) but presented a better objective response rate with panitumumab (8.3 % [I + P] vs 3.3 % [I + C]). There were more infusion reactions with cetuximab.

Panitumumab and cetuximab have similar activity when combined with irinotecan as treatment for patients with disease progression with an irinotecan regimen, potentially rescuing the irinotecan activity.