ABSTRACT Introduction: Panitumumab is an EGFR inhibitor approved for use in metastatic refractory colorectal cancer. It is unclear whether patients who have progressed on cetuximab may benefit from subsequent panitumumab therapy. This retrospective analysis was conducted to describe the experience at The Ohio State University with panitumumab including in patients who have progressed on cetuximab. Methods: Patients who received at least 1 dose of panitumumab between September 2006 and December 2011 were identified using the hospital’s pharmacy database. Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 was used to assess responses and Kaplan-Meier curves were used to estimate progression-free survival (PFS) and overall survival (OS). Results: Eighty-seven patients (median age 61 years) were identified. Sixty-seven percent of patients had tumors with wild-type KRAS, 3.4% had tumors with mutated KRAS and the KRAS status was unknown in 29.9%. Twenty-four percent of the patients had an ECOG performance status of 2 or above and 59.8% of patients had received ≥ 2 prior lines of chemotherapy. Thirty-two percent of patients received single-agent panitumumab while 68% received it in combination with chemotherapy. Of the patients with KRAS wild-type tumors, 10 (17.2%) had objective responses (3 complete, 7 partial) and 26 (44.8%) had stable disease. Median PFS and OS were 5.0 and 9.0 months. The presence of a rash, improved ECOG performance status and coadministration with either irinotecan or FOLFIRI, led to a significantly better OS in univariate analysis. Among patients who had clinical benefit with cetuximab, 71% had subsequent clinical benefit with panitumumab therapy. Conclusions: In our single institution analysis of patients who received panitumumab, the number of prior lines of therapy did not significantly affect OS, suggesting that panitumumab retains its efficacy in the 2nd and 3rd line setting. Additionally, panitumumab can benefit patients who previously had clinical benefit with cetuximab.
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