Abdominoperineal resection by the trans‐anal <scp>total mesorectal excision</scp> approach: are we refuting the technology a bit too early?

We read with interest the recent publication on the comparison of outcomes of low anterior resection (LAR) and abdominoperineal resection (APR) using trans-anal total mesorectal excision (taTME) by the Canadian taTME Expert Collaboration [1]. This retrospective analysis highlights the inferior outcomes of patients in the APR group, cautioning against the use of taTME for the same. However, we feel a careful consideration of the following observations might enhance future research on the subject. In general, patients with disease below the pelvic floor (planned for APR) have biologically more aggressive cancers compared to disease above the pelvic floor (planned for LAR). This in combination with technical difficulties with the procedure translates into inferior oncological outcomes for patients undergoing APR. In the current study, the APR subgroup had more advanced tumours (53% Stage III tumours) compared to the LAR subgroup (25% Stage I tumours). There is no description of grade of histological differentiation of the tumours in the two subgroups. There were more patients of higher body mass index in the APR subgroup, possibly associated with technically difficult procedural conduct. The anterior quadrant is the most susceptible for positive circumferential resection margin (CRM) in the traditional technique of APR as emphasized by the MERCURY II study [2]. This part of perineal dissection is often done under compromised vision in the standard technique, possibly accounting for the increased rates of involved CRM and specimen perforations. As per the technique of taTME APR described by the authors, the anterior dissection of the rectum from prostate or vagina is done under direct vision. A pathological description of involved CRM with regard to involved quadrant of specimen in patients with positive CRM would shed more light on the pathophysiology of proposed inferior oncological outcomes of taTME APR. Two technical advancements which have been applied in the previous decade to improve the surgical approach for low rectal cancers have been the use of a robotic platform and the use of taTME. Shin et al. [3] have shown that careful application of both these techniques leads to superior quality of TME, even in ‘technically challenging or high-risk patients’ (tumour height less than 4 cm, male narrow pelvis, body mass index more than 25 kg/m2). While the learning curve for the robotic approach has been standardized globally, the same is needed for the taTME platforms. A previous report on inferior outcomes following taTME by the Norwegian group attributes the poor outcomes to the pneumo-perineum resulting in increased tumour dissemination and subsequently increased characteristic local recurrence patterns [4]. More clarity on the patterns of recurrence would help identify the technical failures, if any. Future studies validating the role of taTME in low rectal cancers need to specifically recruit and analyse the subgroup of patients at high risk of suboptimal surgery using a traditional approach. Comparison in a homogeneous cohort planned for the same surgery (APR) would be more prudent. Results from the COLOR III trial would shed more light on the role of trans-anal procedures in comparison to standard laparoscopic procedures [5]. Author roles: Conceptualisation: Swapnil Patel, PrudviRaj Data duration.: Swapnil Patel Formal analysis: Prudvi Raj Methodology: Durgatosh Pandey Supervision: Durgatosh Pandey Writing original draft: PrudviRaj Writing- reviewing: Swapnil Patel. None. Data sharing not applicable to this article as no datasets were generated or analysed during the current study.

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