Inclusion Criteria:

- Written informed consent must be given

- Patient ≥ 18 years

- Histologically proven and measurable metastatic adenocarcinoma of the colon or rectum
(according to modified RECIST criteria v.1.1)

- Patients eligible for Erbitux and FOLFIRI treatment K-Ras wild type tumour

- Metastatic disease

- Life expectancy of at least 12 weeks

- WHO performance status of 0 or 1

- Effective contraception for both male and female patients if the risk of conception
exists

- Adequate organ function

- Adequate bone marrow, hepatic and renal function (Hemoglobin > 10.0 g/dL, platelet
count > 100 x 109/L, absolute neutrophil count > 1.5 x 109/L; ALAT, ASAT < 2.5 x ULN
(upper limit of normal range) or < 5x ULN in case of liver metastasis; Alkaline
phosphatase < 2.5 x ULN; Total bilirubin < 1.5 x ULN; Creatinine clearance > 50
mL/min (calculated according to Cockcroft and Gault formula)).

Exclusion Criteria:

- Prior treatment for metastatic disease (adjuvant therapy with 5-FU/oxaliplatin based
regimens) allowed if stopped 6 months prior to registration on study

- Prior treatment with EGFR inhibitor

- Surgery (excluding diagnostic biopsy) or irradiation within 4 weeks prior to study
entry

- Administration of any investigational drug or agent/procedure, i.e. participation in
another trial within 4 weeks before beginning treatment with study drugs

- Concurrent chronic systemic immune therapy, chemotherapy, radiation therapy or
hormone therapy not indicated in the study protocol

- Any active dermatological condition > grade 1 at baseline possibly interfering with
or influencing the results or conduct of the present study

- Brain metastasis (known or suspected)

- Significant impairment of intestinal resorption (e.g. chronic diarrhea, inflammatory
bowel disease)

- Any other uncontrolled concomitant illness, including serious uncontrolled
intercurrent infection

- Severe or uncontrolled cardiovascular disease (congestive heart failure NYHA III or
IV, unstable angina pectoris, history of myocardial infarction within the last twelve
months, significant arrhythmias)

- Known allergy or any other adverse reaction to any of the study drugs or to any
related compound.

- Any organ allograft requiring immunosuppressive therapy.

- Pregnancy (absence to be confirmed by serum/urine beta human chorion gonadotrophin
(HCG)) or breast-feeding.

- Other previous malignancy within 5 years, with exception of a history of a previous
basal cell carcinoma of the skin or pre-invasive carcinoma of the cervix surgically
cured or adequately treated.

- Known drug abuse / alcohol abuse

- Legal incapacity or limited legal capacity

- Any psychological, familial, sociological or geographical condition potentially
hampering compliance with the study protocol and followup schedule; those conditions
should be discussed with the patient before registration in the trial.

- Medical or psychological condition which, in the opinion of the investigator, would
not permit the patient to complete the study or meaningfully sign informed consent.

- Known M. Meulengracht (Gilbert´s disease) or DPD-insufficiency

- Known coagulation disorders

- Ongoing or planned treatment with coumarin derivates