Predictability of antitumor efficacy of cetuximab plus irinotecan based on skin rash severity according to observation period in patients with metastatic colorectal cancer following failure of fluorouracil, irinotecan and oxaliplatin

The efficacy of cetuximab correlates with the severity of skin toxicity, although its onset may vary. The AIM of this retrospective study was to investigate the optimal observation period for skin rash as a predictor of the efficacy of cetuximab plus irinotecan. The subjects comprised 33 patients with KRAS wild-type metastatic colorectal cancer (mCRC) who had received prior chemotherapy with fluorouracil, irinotecan and oxaliplatin. The response rate (RR), progression-free survival (PFS) and overall survival (OS) were compared according to the presence or absence of ≥grade 2 skin rash within 2, 4, 6, or 8 weeks following cetuximab initiation. The overall RR was 45% (15/33) and the median PFS and OS were 188 and 383 days, respectively. A total of 26 patients experienced ≥grade 2 skin rash within 8 weeks. The proportion of responders among patients who developed ≥grade 2 skin rash (severe group) decreased depending on the duration of the observation period (50% within 8 weeks), whereas the proportion of non-responders among patients with