Tumor KRAS status predicts responsiveness to panitumumab in Japanese patients with metastatic colorectal cancer

Abstract

Objective: Mutation status of the KRAS gene in tumors has been shown to be a predictive biomarker of response to anti-epidermal growth factor receptor antibody therapy in patients with metastatic colorectal cancer. This retrospective analysis examined the association between efficacy and safety of the fully human anti-epidermal growth factor receptor antibody panitumumab and KRAS mutation status in Japanese metastatic colorectal cancer patients using data from two clinical trials with adherence to good clinical practices. Methods: An exploratory, integrated analysis of data from KRAS evaluable patients enrolled in a Phase 1 study (Study 20040192) and a Phase 2 study (Study 20050216) was performed. Paraffin-embedded tumor samples were analyzed for KRAS status. Primary efficacy endpoint of this analysis was objective tumor response per modified response evaluation criteria in solid tumors; a key secondary endpoint was progression-free survival. Safety endpoints included incidence of adverse events. Results: Tumor samples with known KRAS status were available from 8 of 13 (62%) metastatic colorectal cancer patients in the Phase 1 study and 16 of 53 patients (30%) in the Phase 2 study. Overall, 14 (58%) patients had wild-type KRAS tumors and 10 (42%) patients had mutated KRAS tumors. Four (17%) patients had a partial response; all responders had tumors with wild-type KRAS. Results of all secondary efficacy endpoints also favored patients with wild-type KRAS. Treatment-related adverse events were predominantly mild to moderate and skin related, and were similar between patients with tumors with wild-type and mutated KRAS in this small patient population. Conclusions: Mutated KRAS status in tumors of Japanese patients with metastatic colorectal cancer is associated with lack of response to panitumumab therapy. © The Author (2010). Published by Oxford University Press. All rights reserved.