Abstract
Cetuximab-induced skin toxicity (Cet-ST) is positively associated with outcome in metastatic colorectal cancer (mCRC). Besides its predictive relevance for targeted therapy, we investigated its prognostic impact with early tumor shrinkage (ETS) ≥20%, another on-treatment surrogate for clinical outcome in FIRE-3. FIRE-3 evaluated first-line FOLFIRI (folinic acid, fluorouracil and irinotecan) plus cetuximab (FOLFIRI/Cet) versus FOLFIRI plus bevacizumab (FOLFIRI/Bev) in mCRC patients with RAS-WT tumors (i.e. wild-type in KRAS and NRAS exons 2-4). Retrospective data on Cet-ST that occurred during cycles 1-3 of treatment were correlated with efficacy endpoints, including ETS. To control for guarantee-time bias, only patients who had completed three or more treatment cycles were considered. Of 199 patients treated with FOLFIRI/Cet, 181 (91.0%) completed three or more treatment cycles. A significant survival benefit of FOLFIRI/Cet over FOLFIRI/Bev was only evident in patients developing Cet-ST grade 2-3 [41.0 versus 26.6 months; hazard ratio (HR)= 0.73; 95% confidence interval (CI): 0.61-0.87; P < 0.001] compared with Cet-ST grade 0-1 (HR= 0.90; 95% CI: 0.67-1.20; P= 0.48). Regarding prognosis, Cet-ST grade 2-3 (n= 75; 41.4%), compared with Cet-ST grade 0-1 (n= 106; 58.6%), was associated with prolonged overall survival (OS; HR= 0.62; 95% CI: 0.42-0.91; P=0.01). In multivariate analysis, both Cet-ST (HR= 0.66; 95% CI: 0.50-0.87; P= 0.003) and ETS (HR= 0.55; 95% CI: 0.41-0.74; P < 0.0001) were independently prognostic for OS. Absence of both Cet-ST grade ≥2 and ETS identified a subgroup of patients with very poor prognosis (median OS 15.1 months). In FIRE-3, the addition of cetuximab to FOLFIRI was associated with superior OS compared with FOLFIRI/Bev only in patients developing Cet-ST grade ≥2. Regarding prognostic relevance, both Cet-ST and ETS were independent and early predictors of survival. The present analysis supports that a combined evaluation of on-treatment parameters such as Cet-ST and ETS may help to guide treatment of mCRC.
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