Before the start of induction therapy:

        Inclusion Criteria:

          -  Histological proof of colorectal cancer (in case of a single metastasis, histological
             or cytological proof of this lesion should be obtained);

          -  Distant metastases which are either technically unresectable or no chance to reach NED
             (patients with only local recurrence are not eligible);

          -  Measurable disease (> 1 cm on spiral CT scan or > 2 cm on chest X-ray; liver
             ultrasound is not allowed). Serum CEA may not be used as a parameter for disease
             evaluation;

          -  Ongoing or planned first line induction therapy with 8 cycles of FOLFIRI or mFOLFOX6.

        Exclusion criteria

          -  Prior adjuvant treatment for stage II/III colorectal cancer ending within 6 months
             before the start of induction treatment

          -  Any prior adjuvant treatment after resection of distant metastases

          -  Previous systemic treatment for advanced disease

          -  RAS mutant mCRC

        At randomisation:

        Inclusion criteria:

          -  WHO performance status 0-1 (Karnofsky PS > 70%);

          -  Disease evaluation with proven SD, PR or CR according to RECIST after 8 cycles of
             FOLFIRI or mFOLFOX6;

          -  Laboratory values obtained ≤ 2 weeks prior to randomisation: adequate bone marrow
             function (Hb > 8.0 mmol/L, absolute neutrophil count > 1.5 x 109/L, platelets > 100 x
             109/L), renal function (serum creatinine ≤ 1.5x ULN and creatinine clearance, Cockroft
             formula, > 30 ml/min), liver function (serum bilirubin ≤ 2 x ULN, serum transaminases
             ≤ 3 x ULN without presence of liver metastases or ≤ 5x ULN with presence of liver
             metastases);

          -  Life expectancy > 24 weeks;

          -  Age: 18-75 years;

          -  Negative pregnancy test in women with childbearing potential;

          -  Expected adequacy of follow-up;

          -  Institutional Review Board approval;

          -  Written informed consent Exclusion criteria

          -  Chronic active infection;

          -  Any other concurrent severe or uncontrolled disease preventing the safe administration
             of study drugs;