Hypothesis

aDepartment of Epidemiology, Istituto di Ricerche Farmacologiche Mario Negri bOccupational Health, Universita` di Milano, Italy Correspondence to Professor Carlo La Vecchia, MD, Istituto Mario Negri, Via G. La Masa, 19, Milano 20156, Italy Tel: +39 02 3901 4527; fax: +39 02 3320 02321; e-mail: [email protected] Received June 20, 2011 Accepted June 24, 2011