Transanal Total Mesorectal Excision: Will It Be A Valid Alternative in Rectal Cancer Surgery?
We have read a recent article by Fernandez-Hevia and Lacy et al1 published in Annals of Surgery with great interest. We sincerely congratulate and admire their pioneering work in the development of this novel rectal cancer surgery—transanal total mesorectal excision (TME), which was opposite to the conventional transabdominal TME and was named “bottom to up TME” by Bill Heald in an editorial.2
Transanal TME has been developed as an explorative solution to the difficult anatomy encountered by laparoscopic rectal cancer surgery, especially in narrow pelvis on an obese male. After a series of preclinical experiments on animals and cadavers, this concept was first put into reality by Lacy and Sylla using a transanal TEM (transanal endoscopic microsurgery) technique with assistance of conventional laparoscopic surgery.3 Colorectal surgeons around the world quickly took great interest in the new operating method, and several centers had successfully performed the new surgery in a similar way with either TEM technique or TAMIS (transanal minimally invasive surgery) technique. High expectations were given to transanal TME because its safety and feasibility has been proven among these studies. Furthermore, it was assumed to be superior to conventional surgery with the following advantages: facilitating distal rectal mobilization to achieve precise and sufficient distal margin, ensuring better functions as neurovascular bundles can be visualized more clearly, and reducing the need for multiple stapler firings in transecting the rectum as the specimen can be extracted through the anus, which also embodied the concept of natural orifices transluminal endoscopic surgery (NOTES). However, only immediate comparisons with laparoscopic surgery like this study or further, randomized control studies in the future can prove its superiority.
In their study, number of patients was increased in the transanal group from 20 in previous reports4 to 37, comparing the short-term outcomes with the other 37 patients who received laparoscopic surgery in a previous period. However, why the comparative group of patients was selected in such a 1:1 ratio was not fully explained. In reality, in regard with the baseline demographic characteristics, the 2 groups were not perfectly matched because patients in the transanal group received neoadjuvant chemoradiation more frequently than those in the laparoscopy group. Therefore, bias might be brought as an influence of preoperative chemoradiation.5 Without doubt, the number of patients who underwent laparoscopic surgical procedure far exceeded that of new surgery, so it may be unreasonable that only a small portion of the former group was included in this comparison. We supposed the author had tried hard to achieve comparability of both cohorts but the detailed statistical methods were not depicted. As a matter a fact, propensity score matching, which has been exploited by many studies,6 is such a method that is utilized to wipe out confounding biases as much as possible, creating randomized-like data between the 2 comparative arms. The discussion on the detailed process of propensity score matching, which needs the help of statistical software, that is, R program, is beyond the scope of this letter. As a matter of fact, a similar study by Velthuis et al7 was published a little earlier in which 25 patients who had undergone the new surgical procedure was compared with the other 25 patients who had undergone conventional laparoscopic surgery. The 2 cohorts were matched only in gender and type of procedure (low anterior resection or abdominoperineal resection).