A randomized, controlled, multicenter, phase I/II study of cetuximab plus irinotecan investigating the pharmacodynamics, genomics and -genetics as well as the safety and efficacy of a dose escalation schedule of cetuximab compared with the standard fixed dosing regimen in patients with irinotecan-

Primary objectives: To compare in skin biopsies the effects of an cetuximab dose escalation regimen on EGFR and downstream signaling pathway markers with those of the standard cetuximab regimen
Primary endpoints: Expression of EGFR and markers for the downstream signalling pathways in normal skin expressed by means of percentage of stained cells and staining intensity. IHC staining will allow a semi quantitative analysis of protein markers of the EGFR related signalling pathway.