Safety and efficacy of panitumumab therapy after metastatic colorectal cancer progression with cetuximab: Experience at a single Japanese institution

Panitumumab (Pmab) is generally considered to be ineffective after the failure of cetuximab (Cmab) therapy in metastatic colorectal cancer (mCRC) patients. However, a few studies have demonstrated that Pmab is an effective treatment for disease progression following Cmab-based regimens in the USA. In the present study, we evaluated the safety and efficacy of Pmab therapy following the failure of Cmab therapy in Japanese patients with mCRC. We performed a retrospective review of the treatment of 16 mCRC patients who tolerated Pmab with clinical benefits after the failure of Cmab therapy between August 2010 and September 2011 at Shiga University of Medical Science. Fourteen of the 16 patients were administered standard Pmab monotherapy (6 mg/kg) intravenously every 2 weeks and the remaining two patients received Pmab with mFOLFOX6 intravenously every 2 weeks. All patients received Pmab chemotherapy until the occurrence of disease progression. Partial radiographic responses (PR) were observed in 2 of the 16 patients and stable disease (SD) was observed in 5 patients. Nine patients had evidence of progressive disease (PD). According to the KRAS status, 7 of the 13 (53.8%) patients who had wild-type KRAS achieved a high disease control rate (PR + SD). The median progression-free survival (PFS) and overall survival (OS) in the wild-type KRAS patients was 96 and 245 days, respectively. Pmab may be an alternative treatment strategy for Japanese patients with mCRC who have experienced failure with standard Cmab-based therapeutic regimens.