Background and Aims: Thyroid cancer is a common malignant tumor in clinical practice, for which surgery is the main treatment method. Endoscopic radical thyroidectomy via a gasless axillary approach is a feasible, safe and cosmetic surgical option, and is being increasingly carried out in our country. The purpose of this study was to investigate the learning curve of endoscopic radical thyroidectomy via a gasless axillary approach, and summarize the course of familiarizing and mastering this new procedure for surgeons, so as to provide a reference for the promotion and development of this procedure. 
Methods: The clinical data of 40 patients with thyroid cancer undergoing total endoscopic radical thyroidectomy via a gasless axillary approach consecutively admitted from January 2019 to June 2020 were retrospectively analyzed. The changing trend graph of operative time and the CUSUM learning curve were modeled and analyzed, and the cut-off value of the learning curve was identified. Taking the cut-off value of the CUSUM learning curve as the threshold, the learning curve was divided into two stages, and then the general information and relevant clinical variables of patients in the two stages were compared.
Results: In the 40 patients, the operative time ranged from 65 to 150 min, with an average operative time of (107.50±26.38) min. The changing trend graph of operative time demonstrated that the operative time displayed an overall descending trend as the number of cases of operation increased. The fitting CUSUM curve reached a maximum value at the cumulative number of cases of operation up to 22. Taking the 22nd operated patient as the demarcation, the learning curve was divided into learning improvement stage and proficient mastery stage. There were no significant differences in terms of the general data between patients in learning improvement stage group (22 cases) and proficient mastery stage group (18 cases) (all P>0.05). The operative time of learning improvement stage group was significantly longer than that in proficient mastery stage group (129.09 min vs. 81.11 min, P<0.001). There were no significant differences with regard to the intraoperative blood loss, postoperative incision pain score, length of postoperative hospital stay and incidence of postoperative complications between the two groups (all P>0.05).
Conclusion: There is a significant learning curve for learning total endoscopic radical thyroidectomy via a gasless axillary approach. Mastering this procedure requires the accumulation of at least 22 operations. It is hoped that the results of this study can provide certain theoretical basis and help for general surgeons to uneventfully go through the plateau of the learning curve (transition from the learning improvement stage to the proficient mastery stage), and then familiarize and master this procedure.