Defining the learning curve for transanal total mesorectal excision for rectal adenocarcinoma.

Background: Early observational data suggest that this approach is safe and feasible, but it is technically challenging and the learning curve has not yet been determined. The objective of this study was to determine the number of cases required achieve proficiency in transanal total mesorectal excision (TA-TME) for rectal adenocarcinoma.

Methods: All TA-TME cases performed from 03/2012-01/2017 at a single high-volume tertiary care institution for rectal adenocarcinoma were included. A cumulative summation (CUSUM) analysis was performed to determine the number of cases required to reach proficiency, defined as high-quality TME (complete or near-complete mesorectal envelope, negative distal (DRM), and circumferential resection (> 1 mm; CRM) margin). The acceptable and unacceptable rates of good quality TME were defined based on the incidence of high-quality TME in laparoscopic (unacceptable rate = 81.7%) and open (acceptable rate = 86.9%) arms of the ACOSOG Z6051 trial.

Results: A total of 87 consecutive cases were included with mean tumor height 4.8 cm (SD 2.7) and 80% (70/87) received neoadjuvant chemoradiation. Post-operative morbidity occurred in 44% (38/87) of cases, including 21% (18/87) readmissions. Median length of stay was 4 days [IQR 3-8]. A good quality TME was performed in 95% (83/87) of cases including 98% (85/87) negative CRM, 99% (86/87) negative DRM, and 99% (86/87) complete or near-complete mesorectal envelope. CUSUM analysis reported that the good quality TME rate reaches an acceptable rate after 51 cases overall, and 45 cases if abdominoperineal resections are excluded.

Conclusion: TA-TME is a complex technique that requires a minimum of 45-51 cases to reach an acceptable incidence of high-quality TME and lower operative duration.