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Clinical trials have evaluated the use of the EGFR inhibitor panitumumab alone and in combination with chemotherapy for the treatment of metastatic colorectal cancer (mCRC). The results of these trials have shown improvements in clinical outcomes with panitumumab, including progression-free survival and overall survival. Although the results were not always significant, these trials highlight the importance of RAS testing to inform treatment decisions, believes Heinz-Josef Lenz, MD.
In May 2014, the FDA approved panitumumab in combination with chemotherapy as a frontline treatment for patients with KRAS wild-type mCRC, based on findings from two phase III clinical trials. In conjunction with panitumumab, the FDA has also approved a companion diagnostic for the detection of the KRAS exon 2 mutation.
Panitumumab has also been evaluated in combination with chemotherapy in patients with mCRC who received prior chemotherapy. In this setting, the addition of panitumumab improved response rate and progression-free survival in patients with wild-type tumors, notes Marwan Fakih, MD.
Comparatively low response rates are observed with second-line panitumumab versus first-line treatment, notes John L. Marshall, MD. This difference in response rates may be due in part to early treatment, tumor size, and changes in the use of imaging, believes Alan P. Venook, MD. Moreover, when a patient experiences disease progression, the characteristics of the tumor after progression may be different from the characteristics of the original tumor, Venook states. To address this, a rebiopsy may need to be performed following progression.