[1] Univ Sheffield, Sch Med & Biomed Sci, Acad Surg Oncol Unit, Sheffield S10 2RX, S Yorkshire, England
[2] Guys Hosp, London SE1 9RT, England
[3] Inst Canc Res, Sect Clin Trials, ICR Clin Trials & Stat Unit ICR CTSU, Sutton SM2 5NG, Surrey, England
[4] Charing Cross Hosp, London W6 8RF, England