Retrospective cohort study on the safety and efficacy of panitumumab for patients with metastatic colorectal cancer: The HGCSG1002 study—Analysis of after cetuximab refractory.
541 Background: In the previous studies, panitumumab (Pmab) has been demonstrated the efficacy for patients with metastatic colorectal cancer (mCRC) in all treatment lines. It is still controversial about the efficacy of Pmab for patients that had progressed on prior cetuximab (Cmab), though there had been a few reports (from Metges et al. and Wadlow et al.) regarding the efficacy of Pmab after Cmab refractory or intolerance. To evaluate the efficacy and safety of Pmab in patients with cetuximab-refractory mCRC, in comparison with anti-EGFR antibody naïve patients (Cmab-naïve) and Cmab-refractory or intolerance patients (prior-Cmab). Methods: Two hundred patients with mCRC treated by Pmab contained chemotherapy were retrospectively registered from 20 centers in Japan (HGCSG 1002 study). Of these, the patients that were refractory to or intolerant for 5-FU/ irinotecan/ oxaliplatin, and were administered Pmab monotherapy were included in this analysis. Results: Of 93 patients (44 prior-Cmab and 49 Cmab-naïve) were evaluated. There were no significant differences in the baseline characteristics of the patients in each group. The incidence of Grade 3 or higher any skin toxicities were higher in the Cmab-naïve (26.5.%) than in the prior-Cmab (11.4%). The overall response rate (RR) was not significantly difference (prior-Cmab/ Cmab-naïve, 9.1%/ 10.2%), but the disease control rate (DCR) was slightly higher in Cmab-naïve group (38.6%/ 55.1%, p=0.15). Progression free survival (PFS) and overall survival (OS) were follows: prior-Cmab/ Cmab-naïve, 2.8m/ 3.1m, 6.8m / 9.5m. There was a significant difference between the two groups in OS curve (p=0.04). Conclusions: Pmab was safely administered to heavily pretreated mCRC patients in daily practice. Although there were no significant differences in RR, DCS and PFS between prior-Cmab and Cmab-naïve, but the median OS was longer for the Cmab-naïve group compared with the prior-Cmab group. Therapeutic efficacies of Pmab for prior-Cmab patients did not comparable to those for Cmab-naïve patients. We are now performing a phase II trial on the efficacy of Pmab for Cmab-refractory mCRC patients.