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 <grade 2 skin rash (mild group) increased (71% within 8 weeks). Similarly, the proportion of patients with an unfavorable prognosis (PFS <6 months, OS <1 year) in the mild group increased (86% for PFS and 71% for OS within 8 weeks), whereas the proportion of those with a favorable prognosis in the severe group remained stable (73% for PFS and 62% for OS within 8 weeks). Therefore, the absence of ≥grade 2 skin rash within 8 weeks may be predictive of unfavorable efficacy of cetuximab plus irinotecan in mCRC patients.