1 Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands.
2 Department of Laboratory Medicine, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands.
3 Department of Medical Oncology, University Medical Center Groningen, University of Groningen, Groningen, the Netherlands. Electronic address: s.oosting@umcg.nl.