1. Gastrointestinal Malignancy Section, Thoracic and Gastrointestinal Oncology Branch, Center for Cancer Research, National Cancer Institute; National Institutes of Health; Bethesda Maryland
2. Division of Cancer Control and Population Sciences, National Cancer Institute; National Institutes of Health; Bethesda Maryland
3. Information Management Services Inc; Calverton Maryland
4. Division of Cancer Epidemiology and Genetics, National Cancer Institute; National Institutes of Health; Bethesda Maryland