Endosonography-guided fine-needle aspiration versus "key-hole biopsy" in the diagnostics of upper gastrointestinal subepithelial tumors. A prospective randomized interventional study - Zoundjiekpon, V; Falt, P; Fojtik, P (Biomed Pap Med Fac Univ Palacky Olomouc Czech Repub, 2020)