1 Surgical and Interventional Trials Unit, Division of Surgery and Interventional Science, Faculty of Medical Sciences, University College London, 1 Euston Square, 40 Melton Street, London NW1 2FD, UK.
2 Cambridge Breast Unit, Addenbrooke's Hospital, Cambridge, UK.
3 School of Medicine, Anglia Ruskin University, Cambridge and Chelmsford, UK.