Irinotecan combined with Panitumumab or cetuximab as third-line treatment for metastatic colorectal cancer.

Abstract

e15551 Background: Literature suggests that the addition of cetuximab can overcome the resistance to irinotecan treatment for metastatic colorectal cancer (mCRC). It is unknown if the combination of panitumumab with irinotecan could also revert treatment resistance and offer a better response rate after progression on irinotecan monotherapy. In this study, we aim to compare the impact of panitumumab plus irinotecan (P+I) or cetuximab plus irinotecan (C+I) on overall survival as a third line mCRC treatment. Methods: This is a single institution, retrospective cohort analysis, evaluating the overall survival of mCRC patients exposed to an anti-EGFR antibody plus irinotecan, upon progression on irinotecan monotherapy. Overall survival function was estimated using the Kaplan-Meier method and compared using the log-rank test. Results: We identified 460 patients with mCRC that fulfilled inclusion criteria, treated between July 2008 and April 2018. One hundred eighty-three (183) patients received (I+C), and 277 received (I+P). Upon diagnosis, the median age was 55.9 years (range, 19 - 83 years), with a male to female ratio of 1.3:1. All patients received the combination of irinotecan and anti-EGFR targeting antibodies for at least one cycle (D1 and D15). Partial response occurred in 22.6% of patients [23.5% for (I+C) and 22.0% for (I+P)], and 25,2% had stable disease [27.8% for (I+C) and 23.6% for (I+P)]. Interestingly, response rate in patients with right-sided tumors was 3.3% in the (I+C) regimen and 14.3% in the (I+P) regimen. The disease control rate was 50.3% in the (I+C) combination and 45.7% in the (I+P) combination (p = 0.358). The median overall survival (mOS) for all patients was 9.63 months, 8.97 to the group C+I and 10.74 to P+I (p = 0.73). Regarding primary tumor location, the mOS was 6.34 mo for right-sided tumors and 10.74 mo for left-sided tumors (p = 0.022). The 3-year survival rate was 5.6% for the (C+I) treated patients and 3.2% for (P+I). Conclusions: (P+I) and (C+I) combinations showed similar response rate and mOS as a third-line treatment for mCRC, suggesting that both anti-EGFR agents can be used in this setting. A perceived tendency for a superior response with the (I+P) regimen in right-sided tumors might warrant further investigation in prospective studies.