1 Occupational and Environmental Medicine, National Heart & Lung Institute, Imperial College London, London, UK, Unit of Epidemiology, Department of Preventive Medicine, Fondazione IRCCS Ca' Granda-Ospedale Maggiore Policlinico and Department of Clinical Sciences and Community Health, Università degli Studi di Milano, Milan, Italy, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, Bethesda, MD, USA, Institute for Risk Assessment Sciences, Environmental Epidemiology Division, Utrecht University, Utrecht, The Netherlands and Western Australian Institute for Medical Research, University of Western Australia, Nedlands, WA, Australia.