AIP Conference Proceedings [AIP Publishing INTERNATIONAL SYMPOSIUM ON THE FRONTIERS OF BIOTECHNOLOGY AND BIOENGINEERING (FBB 2019) - Hangzhou City, China (20–21 April 2019)] INTERNATIONAL SYMPOSIUM ON THE FRONTIERS OF BIOTECHNOLOGY AND BIOENGINEERING (FBB 2019) - Clinical efficacy of thoracoscopic and laparoscopic combined radical surgery in the treatment of elderly patients with esophageal cancer and its effect on immunity