 In this phase II double-blind placebo-controlled trial the efficacy and safety of CY-503, 350 ng s.c. injected in patients with chemotherapy refractory MCRC are tested. Approved treatments given to MCRC patients are usually discontinued after a treatment over some weeks at the first detection of objective PD. It will be tested if CY-503 is able to achieve progression-free-survival PFS in comparison to placebo. Patients will initially be included to receive either CY-503 or placebo until documentation of objective PD. 