Adri C Voogd1, Rob H A Verhoeven2. 1. Department of Epidemiology and Department of Medical Oncology, School of Oncology and Developmental Biology (GROW), Maastricht University Medical Centre, Maastricht, The Netherlands; Department of Research, Netherlands Comprehensive Cancer Organisation (IKNL), Utrecht, The Netherlands. Electronic address: adri.voogd@maastrichtuniversity.nl. 2. Department of Research, Netherlands Comprehensive Cancer Organisation (IKNL), Utrecht, The Netherlands.