Kalantzis Ioannis is a Gastroenterologist and Doctor of Medicine at the Medical School of the National and Kapodistrian University of Athens. He serves as a Consultant in the 1st Gastroenterology Clinic of Interventional Endoscopy at IASO Hospital, where he receives patients and performs endoscopic procedures. He graduated from the Medical School of Democritus University of Thrace. He specialized in Internal Medicine at the Pathology-Oncology Clinic of the Unified Anticancer Hospital of Piraeus "Metaxa," managing the full spectrum of pathological and oncological diseases. Subsequently, he completed his Gastroenterology specialty at the General Hospital of Athens "Korgialeneio-Benakeio / Hellenic Red Cross," during which he performed over 3,000 diagnostic and therapeutic endoscopic procedures of the upper and lower gastrointestinal tract and biliary system. He acquired particular expertise in endoscopic polypectomy of the stomach, duodenum, and colon, in endoscopic retrograde cholangiopancreatography (ERCP), in endoscopic gastrostomy placement, as well as in the management and treatment of patients with Inflammatory Bowel Diseases (Crohn's Disease and Ulcerative Colitis). He completed with distinction the Master’s Program (MSc) of the National and Kapodistrian University of Athens titled "Neoplastic Disease in Humans: Diagnosis, Contemporary Therapy, and Research," as well as his Doctoral Thesis (PhD) on "Clinicopathological differences and correlations between cancer of the right and left colon." He has participated in international clinical studies, attended numerous conferences, educational courses, and seminars, and has numerous presentations and publications in Greek and international conferences and journals. Finally, he is a member of the Hellenic Gastroenterology Society and the Hellenic Society for the Study of the Liver.