BackgroundIn the CRYSTAL study adding cetuximab to first-line FOLFIRI significantly improved outcome in patients with KRAS wild-type metastatic colorectal cancer. Quality of life (QoL) was assessed, and associations with tumour response and survival were investigated. Patients and methodsThe European Organization for Research and Treatment of Cancer QoL questionnaire-core 30 was used, focusing on global health status (GHS)/QoL and social functioning scales. Radiological response was assessed by an independent review committee. ResultsQoL was evaluable in 627/666 patients (94%) with KRAS wild-type tumours; of these 52% received FOLFIRI, and 48% FOLFIRI plus cetuximab. Pattern mixture analysis revealed no significant differences for GHS/QoL (P=0.12) and social functioning scores (P=0.43) between the treatment arms. In additional analyses: early skin reactions in patients receiving cetuximab did not significantly affect these QoL scales, and tumour response was more common (58% versus 40%, P=0.0002) and survival longer (Hazard ratio 1.68, P<0.0001) in asymptomatic compared with symptomatic patients at baseline. Adding cetuximab to FOLFIRI was associated with significantly higher tumour response irrespective of patient baseline symptomatic status, and enhanced symptom relief from baseline in those whose tumours had responded. ConclusionAdding cetuximab to FOLFIRI improved response rate and survival without either improving or negatively impacting on GHS/QoL and social functioning.