1. Division of Surgical Oncology, Medical University – Pleven, Bulgaria
2. Student Study-Research Group of Surgical Oncology, Medical University-Pleven, 4, Rila Str., Svishtov, 5250, Bulgaria
3. Student Study-Research Group of Surgical Oncology, Medical University – Pleven, Bulgaria
4. Department of General and Clinical Pathology, Medical University – Pleven, Bulgaria