1. Department of Gastroenterology, Hepatology and Clinical Oncology, Center of Postgraduate Medical Education, W.K. Roentgen street, Warsaw, 02-781, Poland
2. Department of Gastroenterological Oncology, the Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
3. Department of Gastroenterology, Hepatology and Clinical Oncology, Center of Postgraduate Medical Education, Warsaw, Poland
4. Department of Cancer Prevention, the Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Warsaw, Poland
5. Institute of Health and Society, University of Oslo, Oslo, Norway