Sensitivity to previous irinotecan treatment does not predict the efficacy of combination chemotherapy with cetuximab plus irinotecan for wild-type KRAS metastatic colorectal cancer

The aim of this study was to evaluate the association of sensitivity to previous irinotecan-based chemotherapy with efficacy of cetuximab plus irinotecan therapy in metastatic colorectal cancer (MCRC) patients with wild-type KRAS. We analysed a pooled data set consisting of data from 87 MCRC patients from two previous phase II studies (n = 60) and a group given off-protocol treatment (n = 27) following irinotecan-, oxaliplatin-, and fluoropyrimidine-based chemotherapy. Overall objective response rate to cetuximab plus irinotecan was 28.7%, median progression-free survival (PFS) was 5.3 months, and median overall survival was 12.2 months. Objective response rate did not significantly differ between patients with a favourable response to previous irinotecan (n = 23), stable disease (n = 38), or progressive disease (n = 26), with observed rates of 29.2%, 31.6%, and 23.1%, respectively. Additionally, the non-parametric Spearman rank correlation coefficients (ρ) between the PFS of previous irinotecan-based chemotherapy and that of cetuximab plus irinotecan were quite low (ρ = 0.067 and 0.057 in patients with previous irinotecan as first- and second-line therapies, respectively). Although exploratory nature and small sample size may be limitations of this study, these findings indicate that the efficacy of irinotecan plus cetuximab in MCRC patients with wild-type KRAS did not differ by previous sensitivity to irinotecan.