In this study, we evaluated whether RS has technical superiority over LS for ultra-low rectal cancer by comparing LAR frequency in patients who underwent SPOs. Compared to LS, RS was significantly associated with an increased frequency of LAR in SPOs for ultra-low rectal cancer. Our findings support the argument that RS has technical superiority over LS for ultra-low rectal cancer treatment.
Minimally invasive surgery for low rectal cancer requires highly advanced surgical skills. The lower the tumor is located in the deep and narrow pelvis, the more technically challenging the procedure becomes. Previously, APR was the standard procedure for low rectal cancers within 5 cm of the AV [16, 26, 27]. However, ISR is now widely recognized as an acceptable SPO procedure [28]. Moreover, recent advances in surgical techniques have made it possible to perform LAR, including partial excision of the internal anal sphincter, via a transabdominal approach for ultra-low rectal cancer [17, 29].
That said, LAR for ultra-low rectal cancer requires mobilization of the rectum, even in the anal canal, by the transabdominal approach, which still requires highly advanced surgical techniques. Therefore, the technical superiority of RS over LS could be evaluated by comparing the frequency of LAR between these two types of SPOs for ultra-low rectal cancer. To the best of our knowledge, no previous study has attempted to compare the types of SPOs between LS and RS for ultra-low rectal cancer. In contrast to previous reports, we excluded APR, the indications of which are determined by the tumor and technical and non-technical factors, such as preoperative anorectal dysfunction and tolerance of postoperative defecatory dysfunction. As such, the types of SPOs utilized for the patients herein were determined largely based on technical factors, which is also a strong point of our study.
In this study, LAR frequency was significantly higher in the RS group (67.6%) than in the LS group (48.8%), and multivariate analyses showed that RS and the tumor distance from the AV were significantly associated with an increased frequency of LAR for ultra-low rectal cancer. Furthermore, there were no significant differences in the postoperative complications or the pathological results between the RS and LS groups. Although the operation time was longer in the RS group, this was attributed to the higher proportion of patients who underwent LLD in the RS group. Hence, compared to LS, RS allows transection of the distal rectum for ultra-low rectal cancer via the transabdominal approach, without compromising surgical and pathological outcomes. These findings suggest that RS has technical superiority over LS for ultra-low rectal cancer. This superiority can be attributed to the technology involved in RS, such as digital suppression of hand tremors, free-moving multi-joint forceps, and high-quality three-dimensional visualization. Furthermore, the robotic stapler may be advantageous during stapling owing to its good maneuverability [30, 31].
In addition to the transabdominal approach, TaTME has been used for rectal cancer [32]. It has been reported that the transanal approach could enhance access to the distal part of the rectum and enable better visualization making a more accurate oncological dissection possible [33, 34]. However, early adopters of TaTME underscored its technical difficulty. Several studies examining TaTME registry data have revealed that patients sustained visceral injuries during perineal dissection [35, 36]. Additionally, Wasmuth et al [37]. demonstrated that the oncological outcomes after TaTME were inferior to the national results. Further investigation is required to evaluate the long-term oncological results of TaTME. In contrast, RS makes it possible to perform surgery safely and precisely, even for ultra-low rectal cancer via the transabdominal approach, which is commonly used for TME. Since RS is performed in a familiar transabdominal field-of-view, it is easy to recognize the anatomy and the surgery can be performed safely even in the deep pelvis. Furthermore, several studies have indicated good long-term results [2, 11, 38].
This study has several limitations. First, this was a retrospective study performed at a single institution. Second, long-term outcomes were not investigated. Randomized controlled trials are necessary to validate our findings. Third, although this study focused on the technical aspects, it was unclear whether LAR or ISR is better in terms of postoperative anorectal function. Previous studies have reported that patients who have undergone ISR have a higher risk of fecal incontinence and bowel dysfunction than those who have undergone LAR [39, 40]. However, the characteristics of patients in previous studies were different from those in this study, and these results could not be extrapolated to the present study. Further studies are necessary to clarify the effects on postoperative anal function.