Department of Oncology, University of Oxford, CB2 0QQ, Oxford, United Kingdom. Leiden University Medical Center, Leiden, The Netherlands. Division of Medical Oncology, Department of Oncology, Schulich School of Medicine and Dentistry, Western University, London, ON, Canada. Warwick Clinical Trials Unit, University of Warwick, CV4 7AL, Coventry, United Kingdom. University of Manchester and Christie NHS Foundation Trust, M20 4BX, Manchester, United Kingdom. Experimental Cancer Medicine Centre, OX3 7DQ, Oxford, United Kingdom. Cambridge Cancer Trials Centre, Cambridge University Hospitals NHS Foundation Trust, CB2 0QQ, Cambridge, United Kingdom. Section of Epidemiology and Biostatistics, Leeds Institute of Cancer and Pathology, University of Leeds, LS9 7TF, Leeds, United Kingdom. Department of Oncology, University of Oxford, CB2 0QQ, Oxford, United Kingdom. mark.middleton@oncology.ox.ac.uk. NIHR Biomedical Research Centre, OX3 7LE, Oxford, United Kingdom. mark.middleton@oncology.ox.ac.uk. Cambridge Cancer Centre, Cambridge University Hospitals NHS Foundation Trust, CB2 0QQ, Cambridge, United Kingdom.