Aims and background: Few data describe the activity of panitumumab after cetuximab-irinotecan-based regimen failure in patients with KRAS wild-type metastatic colorectal cancer (WT MCRC).
Methods: The aim of this study is to assess if panitumumab has some activity in this setting.
Results: We retrospectively analyzed 25 patients with KRAS WT MCRC who received panitumumab from July 2009 to January 2013 after progression on cetuximab. All patients had previously received cetuximab and irinotecan (20 patients) or oxaliplatin (5 patients). We withdrew cetuximab for intolerance in 4 patients (16%). Twenty-one patients (84%) who had previously responded to cetuximab (overall response rate [ORR] plus stable disease ≥5 months) received panitumumab off-label after progression on cetuximab because they were strongly motivated to continue treatment without chemotherapy. The median number of cycles of panitumumab was 7 (range 1-54). Only 20 patients were evaluable for ORR (5 patients received 1-2 cycles and then died). We observed 1 (5%) partial response, 5 (25%) stable disease, median duration 9 months. Median progression-free survival (PFS) and overall survival (OS) were 5 (3-28) and 8 (5-41) months, respectively. All patients were evaluable for toxicity. No patients developed anemia or neutropenia. One patient (4%) developed grade 2 thrombocytopenia, 8 patients (32%) grade 2-3 dry skin or rash, and 2 patients (8%) grade 2 nausea-vomiting (Common Terminology Criteria for Adverse Events version 4.03).
Conclusions: Our data, with all the limits of a retrospective analysis, show longer PFS and OS as compared to other series in the same setting, demonstrating that panitumumab has treatment effectiveness in patients with KRAS WT MCRC who progressed on prior cetuximab. Further confirmatory prospective studies with a larger series of patients are necessary.