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

Purpose: 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.

Methods: 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.

Results: 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.

Conclusions: 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.