1. Department of Surgery, Royal Postgraduate Medical School, Hammersmith Hospital, Du Cane Road, London W12 ONN, U.K.
2. Department of Surgery, School of Postgraduate Medicine and Biological Sciences, University of Keele, Thornburrow Drive, Stoke-on-Trent ST4 7QB, U.K.
3. Department of Histopathology, St Mary's Hospital Medical School, Norfolk Place, London VV2 1PG, U.K.