Previous RCTs have demonstrated that the short-term and long-term oncological outcomes of CLS for rectal cancer are comparable to those of OS [1–4]. With the advent of RALS as the latest MIS, studies have been conducted to evaluate whether its application can overcome the limitations of CLS for rectal cancer. Many studies have shown that the surgical outcomes of RALS are comparable to those of CLS [10–12, 15–18, 23–29], although the proportion of patients receiving NCRT in those studies were variable and relatively low [11, 23]. In the present study, we evaluated the potential advantages of RALS after NCRT for rectal cancer by comparing operative and pathological outcomes between RALS and CLS in rectal cancer patients. The fact that we performed propensity score-matched analysis to obviate the possibility of selection bias and to adjust for significant differences in baseline characteristics of rectal cancer patients is a strength of our study.
The conversion rate to laparotomy of MIS reflects its technical complexity. Achieving a low conversion to open laparotomy rate is clinically important, because patients converted to open laparotomy are more likely to develop postoperative complications and local recurrence [30, 31]. The conversion rates of CLS for rectal cancer typically ranged from 9 to 16% in large RCTs [2, 5, 6], and can be as high as 25% in patients with rectal cancer receiving NCRT . Although the ROLARR trial failed to indicate the superiority of RALS over CLS in terms of the conversion rate to open laparotomy (8.1% vs 12.2%, p = 0.16) , several meta-analyses have reported a lower conversion rate for RALS compared with CLS [25, 26, 28, 29]. In our study, no conversion was noted in the RALS group, and only one patient (1.2%) required conversion to open laparotomy due to tumor-related factors in the CLS group in the overall cohort. These results were not uncommon for RALS, but were favorably comparable to the conversion rate of CLS for rectal cancer in the COREAN trial . However, since we have been performing CLS for locally advanced rectal cancer after administering NCRT since 2011, our low conversion rate to laparotomy of CLS for rectal cancer might reflect our abundant and advanced expertise.
Several previous studies have shown that RALS for rectal cancer is associated with a significantly longer operative time compared with CLS for rectal cancer [16, 23, 28, 29]. Inconsistent with the results of previous studies, median operative times were comparable between the groups in our study. Moreover, the present study included the learning curve period, which was previously reported as ranging from 20 to 44 cases [18, 32, 33]. After overcoming this learning curve and acquiring adequate expertise, such as in the working of the camera and manipulation of robotic forceps, and with practice in the set up for the robotic system, our operative time might become shorter than reported here.
Although NCRT is an established risk factor for postoperative complications, the complication rate in our study was comparable to the previously reported rates of 8.9–33.1% and 18.4%-31.7% for RALS and CLS, respectively [10, 12, 17, 18, 24, 27]. Postoperative complication (CD grade ≥ II) rates in the RALS group were significantly lower than those of CLS in this study. The superiority of RALS in terms of postoperative complications could be mainly due to the lower occurrence of anastomotic leakage and urinary retention in the RALS group, because there was a tendency to lower rates of these complications in the RALS compared with the CLS group in both cohorts. The frequency of anastomotic leakage in this study was 15.1% in the overall cohort (RALS 0.0% vs. CLS 20.5%) and 9.1% in the matched cohort (RALS 0.0% vs. CLS 25.0%). Previous studies demonstrated that anastomotic leakage occurred in 1.5–12.2% of patients who underwent RALS and 1.8–10.4% of those who underwent CLS [10, 12, 17, 18, 24, 27]. In our study, although the rates of anastomotic leakage in the RALS group were much lower than those in previous reports, leakage rates in the CLS group were extremely high compared with those in previous reports. To evaluate the risk factors for anastomotic leakage, we performed sub-group analyses in the 53 patients who underwent LAR among the overall cohort (RALS: 14 cases, CLS: 39 cases). Eight of the 53 patients had anastomotic leakage > CD grade II, including six male (6/31; 19.4%) and two female patients (2/22; 9.1%) (p = 0.2912); two of the patients (2/6; 33.3%) were older than 75 years and six patients (6/47; 12.8%) were aged less than 75 years (p = 0.2298). In terms of intraoperative blood flow assessment with ICG injection, anastomotic leakage occurred in seven patients (7/35; 20.0%) who did not undergo the blood flow test and one patient (1/18; 5.6%) in whom the test was performed (p = 0.1355). Thus, although male sex, elderly age, and not performing the blood flow test were associated with slightly higher rates of anastomotic leakage compared with their counterparts, the differences were not significant. In terms of the surgical approach, on the other hand, eight patients (8/39; 20.5%) who underwent CLS and none of the RALS patients developed anastomotic leakage (p = 0.0201). In terms of BMI, four patients (4/11; 36.4%) with BMI ≥ 26 kg/m2 and four patients (4/42; 9.5%) with BMI < 26 kg/m2 developed anastomotic leakage (p = 0.0418), suggesting that obesity might be a risk factor for anastomotic leakage in patients undergoing CLS.
The frequency of urinary retention in the present study was 4.5% in the overall cohort (RALS 0.0% vs. CLS 6.2%) and 3.3% in the matched cohort (RALS 0.0% vs. CLS 6.7%), showing that the rates of urinary retention in the RALS group tended to be lower than those in the CLS group in both cohorts. Moreover, the days to commencement of a soft diet and duration of postoperative hospital stay were both more favorable in the RALS than the CLS group in both cohorts. Previous studies have reported that RALS offers potential benefits, such as a lower complication rate, shorter postoperative hospital stay, and more favorable functional results, and several factors have been proposed to explain the reason why the robotic approach is more advantageous than the conventional laparoscopic approach for rectal cancer [11, 12, 23, 25–28]. Wristed instruments enable ambidextrous capability and intuitive manipulation by the surgeons, the camera provides stable three-dimensional high-definition imaging, and the robotic arm provides steady retraction and exposure. Combination of these functions in the robotic system facilitates accurate anatomical dissection in the deep and narrow pelvis, and might enable greater preservation of pelvic autonomic functions. The potential advantages of RALS might be more pronounced under specific conditions, such as lower rectal cancer, in male and obese patients, and those undergoing surgery after NCRT [10, 18, 26].
We observed no significant differences in resection margins (proximal and distal), positive RMs, or the number of lymph nodes dissected, between the two groups in both cohorts. Consistent with the above results, analysis of the patients who underwent LAR showed no significant differences in terms of DM between groups in the matched cohorts (RALS: 31.4 ± 15.8 mm, CLS: 28.5 ± 16.1 mm, p = 0.6819, data not shown). The technical and oncological results of the procedure in the present study were comparable between the RALS and CLS approaches. This might suggest that the technical and oncological results of the procedure in CLS for rectal cancer are virtually equivalent to those of RALS, when performed by experienced laparoscopic surgeons. However, further studies are necessary to evaluate the other pathological parameters, such as CRM, which is an important predictor of oncological prognosis .
Our study has some limitations. The first is its non-randomized and retrospective design. To overcome this limitation, we performed case-matched analysis using several clinical variables. Thus, the groups were well balanced and selection bias was obviated. Second, our cohort study was performed at a single center and was relatively limited. Therefore, the number of cases in our study might be insufficient to draw decisive conclusions. Third, our propensity score-matched analysis mainly took baseline characteristics into account, and did not consider latent confounders, such as surgeon’s experience and the learning curve. Fourth, we did not assess postoperative sexual function, which is essential to evaluate the evidence concerning the clinical benefits of a treatment modality, and we only assessed voiding function without using a questionnaire about voiding function. Finally, we evaluated proximal, distal and radial margins as pathological parameters for assessment of the technical and oncological results of the procedure, and not the CRM. Hence, our pathological analysis might be inadequate for assessing the completeness and quality of TME.