Establishment of pure NOTES procedure using a conventional flexible endoscope: review of six cases of gastric gastrointestinal stromal tumors - Mori, H.; Kobara, H.; Kobayashi, M.; Muramatsu, A.; Nomura, T.; Hagiike, M.; Izuishi, K.; Suzuki, Y.; Masaki, T. (Endoscopy, 2011)