1 Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD; Universita' degli Studi di Milano, Milan, Italy (PAB).
2 Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Bethesda, MD; Universita' degli Studi di Milano, Milan, Italy (PAB). caporaso@nih.gov.