AIM: To conduct a meta-analysis to determine the relative merits of robotic surgery (RS) and laparoscopic surgery (LS) for rectal cancer.

METHODS: A literature search was performed to identify comparative studies reporting perioperative outcomes for RS and LS for rectal cancer. Pooled odds ratios and weighted mean differences (WMDs) with 95% confidence intervals (95% CIs) were calculated using either the fixed effects model or random effects model.

RESULTS: Eight studies matched the selection criteria and reported on 661 subjects, of whom 268 underwent RS and 393 underwent LS for rectal cancer. Compared the perioperative outcomes of RS with LS, reports of RS indicated favorable outcomes considering conversion (WMD: 0.25; 95% CI: 0.11-0.58; P = 0.001). Meanwhile, operative time (WMD: 27.92, 95% CI: -13.43 to 69.27; P = 0.19); blood loss (WMD: -32.35, 95% CI: -86.19 to 21.50; P = 0.24); days to passing flatus (WMD: -0.18, 95% CI: -0.96 to 0.60; P = 0.65); length of stay (WMD: -0.04; 95% CI: -2.28 to 2.20; P = 0.97); complications (WMD: 1.05; 95% CI: 0.71-1.55; P = 0.82) and pathological details, including lymph nodes harvested (WMD: 0.41, 95% CI: -0.67 to 1.50; P = 0.46), distal resection margin (WMD: -0.35, 95% CI: -1.27 to 0.58; P = 0.46), and positive circumferential resection margin (WMD: 0.54, 95% CI: 0.12-2.39; P = 0.42) were similar between RS and LS.

CONCLUSION: RS for rectal cancer is superior to LS in terms of conversion. RS may be an alternative treatment for rectal cancer. Further studies are required.

Over the past 30 years, laparoscopic surgery (LS) has revolutionized general surgical practice, above all affecting surgery of the gastrointestinal (GI) tract[1,2]. However, with regard to rectal cancer, there are several technical drawbacks to LS, including limited range of motion of instruments in a narrow pelvic cavity, related loss of dexterity, and an inadequate visual field associated with unstable camera view and assistant’s traction, which are not under the surgeon’s control[3]. Technical advantages of the Da Vinci robotic system could overcome the limitations of LS for rectal cancer, by giving the surgeon a 3D view, better ergonomics, enhanced dexterity, precision and control due to the 3D optical system and EndoWrist^® Instruments.

Although surgical robots have been successfully applied to a number of disciplines, most notably urological and cardiac procedures[4,5], robotic rectal surgery remains in its infancy. Most studies have been limited by small sample size and a single institution design. To overcome these limitations, a meta-analysis of studies comparing robotic surgery (RS) and LS for rectal cancer should be performed. The aim of this meta-analysis was to determine the relative merits of RS and LS for rectal cancer.

Meta-analysis could be used to evaluate the existing li-terature in both qualitative and quantitative ways by comparing and integrating the results of different studies and taking into account variations in characteristics that could influence the overall estimate of the outcome of interest[14]. Although meta-analysis has traditionally been applied and best confined to RCTs, meta-analytical techniques using NRCTs might be a good method in some clinical settings in which either the number or the sample size of RCTs was insufficient[15]. To the best of our knowledge, this was the first comprehensive meta-analysis comparing RS versus LS for rectal cancer.

RS is often perceived as being more time-consuming, because of the additional set-up time required[16]. It usually requires two steps for rectal cancer[17,18]. After dissection of the left colon and sigmoid colon and division and ligation of the inferior mesenteric vessels, the da Vinci system must be moved for the next step. However, moving the da Vinci system is a time-consuming and difficult procedure because the robotic devices are heavy and bulky. This meta-analysis revealed that there was no significant difference in operative time between RS and LS. This finding could be attributable to the shortened learning curve, and it has been suggested that the intuitive controls of robotic systems, more comparable with open surgery, could shorten the learning curve, even in the hands of relatively inexperienced laparoscopic surgeons[19]. As we overcame the learning curve with experience and prevented collisions by properly positioning the robotic ports, the operation time decreased. There was no significant difference in blood loss when comparing RS and LS.

Conversion to open surgery and complications are critical in minimally invasive rectal cancer surgery, because converted patients have higher complication rates[20] and, in one series at least, worse oncological outcomes[21]. Conversion rate was significantly lower in the RS group than in the LS group. Lower conversion with RS might have been due to superior exposure and visualization of the operating field in the pelvis, thanks to the ability of the fixed fourth arm to grip and maneuver organs; the ability of the surgeon to move the 3D camera as required; and the greater ease of dissection afforded by the highly maneuverable EndoWrist instruments attached to the robotic arms.

Number of days to passing flatus was lower in the RS group than the LS group, meanwhile, length of stay was found to be no different between the two groups. However, analysis of the pooled data did not reveal any significant difference in this regard. These findings implied that the time required for patients to resume daily activities might not be shorter after RS than LS. There was no significant difference in complications when comparing RS and LS. On the contrary, it has been postulated that these characteristics of RS could make patients recover faster and reduce complications, because with the da Vinci surgical system, robotic arms are used for retraction and dissection during the total mesorectal excision procedure, and their use reduces unnecessary procedures and minimizes iatrogenic tissue injury during retraction. These findings are difficult to explain, and more advanced studies are needed before such conclusions can be drawn.

We postulated that specimen quality could be used as an indicator to predict long-term clinical oncological results. No significant differences were proved between RS and LS in the pathological details, including harvested lymph nodes, DRM and PCRM. The number of harvested lymph nodes, DRM, and PCRM did not differ significantly between the two groups in our meta-analysis. This demonstrated that RS could be performed safely and with a high success rate following oncological principles compared with LS. However, long-term follow-up evaluation is necessary to evaluate the exact oncological outcomes of RS for rectal cancer.

The cost of RS equipment is very high and likely to be a serious impediment to uptake in the foreseeable future[22]. However, it is important to perform a cost-effectiveness analysis between RS and LS. Only one trial has reported that the average total hospitalization costs were higher in the RS group ($83 915) than in the LS group ($62 601), and these differences were not statistically significant[7]. To the best of our knowledge, total hospitalization costs may be due to the greater expense and consumption of operating room resources such as space and the availability of skilled technical staff, and differ significantly between hospitals[23]. Therefore, insufficient data and great heterogeneity precluded a meta-analysis of cost-effectiveness.

Significant heterogeneity in those articles was observed in the operative time, blood loss, days to passing flatus, length of stay and DRM, which may be explained by the difference in skill, extension of lymph node dissection, and duration of learning curve. Regarding the heterogeneity between the articles, random-effect models were used in this meta-analysis.

The results of the present meta-analysis should be interpreted with caution because of several limitations. First, some data came from NRCTs, and the overall level of clinical evidence was low. It has been reported that NRCTs can either exaggerate or underestimate the magnitude of measured effects in a study of intervention regardless of quality scores[24]. However, Abrahama et al[25] have found that meta-analysis of well-designed NRCTs of surgical procedures was probably as accurate as that of RCTs. In fact, six studies included in the present study were NRCTs. Second, there was heterogeneity between the two groups, because it was impossible to match patient characteristics in all studies. We applied a random-effect model to take into consideration between-study variation, and it might have been expected to exert a limited influence. Finally, authors might be more likely to report positive results, and studies with significant outcomes were more likely to be published, so potential publication bias might have been present.

In conclusion, the results of this meta-analysis of 661 patients show that RS is superior to LS for rectal cancer in terms of conversion. Therefore, RS may be an alternative treatment for rectal cancer. Further studies are required to better define its role.