1. Department of Oncological Gastroenterology, The Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland;
2. Department of Gastroenterology, Hepatology and Clinical Oncology, Poland and Medical Centre for Postgraduate Education, Warsaw, Poland;
3. Department of Microbiology, The Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland;
4. Department of Cancer Prevention, The Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland;
5. Department of Pathology and Laboratory Medicine, The Maria Skłodowska-Curie Memorial Cancer Centre and Institute of Oncology, Warsaw, Poland;
6. Department of Pathomorphology, Medical Centre for Postgraduate Education, Warsaw, Poland