Discussion
Recently, surgery for colorectal cancer is shifting to less invasive surgery because of better postoperative short-term surgical results, which include: Lower postoperative morbidity, reduced intraoperative blood loss, less pain, faster recovery and better quality of life (12,13). Moreover, laparoscopic surgery for colorectal cancer is considered to be comparable to long-term results compared with open surgery (12,13).
SPS for colorectal disease was first described in 2008 (14,15), and has been reported the better short-term surgical outcomes in comparison to MPS since then. However, most of the reports on SPS are concerned with colon cancer (4-6), and whether SPS is better than MPS for rectal cancer still remains unclear.
This systematic review is to compare the clinical outcomes of SPS vs. MPS in patients with rectal cancer. The major findings of this analysis show that SPS for rectal cancer is a safe and feasible approach (as deemed by 16.8% of patients requiring an additional port and 0.8% requiring conversion to open surgery), and yields adequate short-term surgical outcomes (e.g., morbidity of 28.0% and mortality of 2.4%) and satisfactory oncological outcomes (e.g., R0 resection rate of 99.0%).
With regard to operative factors, two studies reported that operative time was significantly longer in the SPS group and two studies reported that the blood loss is significantly less in the SPS group. Kim et al reported that the learning curve of SPS for sigmoid colon cancer was 61-65 cases according to multidimensional statistical analyses (16). Li et al reported that the experienced MPS surgeons achieved the technical competence after the 44th case of SPS plus one port in patients with sigmoid colon cancer and upper rectal cancer (17). SPS for rectal cancer is technically more challenging and require more cases for proficiency, and we consider this result is likely little of statistical significance.
The conversion rate to open surgery was significantly lower in the SPS group than in the MPS group (0.8 vs. 5.4%, P=0.032). However, 16.8% in the SPS group had required an additional port to complete the operation, due to fixation of tumor, severe pelvic fibrosis or distal rectum division. In a previous study, the conversion rate of SPS for rectal cancer was 8% (18). Hirano et al reported that SPS plus one port was safe and feasible for rectal cancer to overcome the technical difficulties, including mobilization and rectum division (19). We suggest that it is most reasonable to insert an additional port at the time when SPS is judged technically difficult.
With regard to postoperative outcomes, the morbidity and mortality rate in the SPS group were 28.0 and 2.4%, respectively, and comparable to the short-term outcomes of conventional laparoscopic surgery for rectal cancer in a recent randomized control trial (20). Anastomotic leakage, reoperation, postoperative hospital stay and readmission were similar in both groups, and also comparable to the above trial.
Reduction of postoperative pain is very important for early recovery, and it is well known that the transition from open surgery to laparoscopic surgery is associated with reduction of postoperative pain. Sourrouille et al (11) and Bulut et al (8) revealed reduction of postoperative pain scores following SPS compared to MPS in their studies. Although it is controversial whether SPS contributes to the reduction of postoperative pain compared with MPS at present, this innovative surgical technique may be involved in postoperative pain reduction.
The maintenance of the surgical oncological outcome is the most important factor in the treatment of rectal cancer. The oncological outcomes, including number of harvested lymph nodes, length of resected specimen, proximal dissection margin, distal dissection margin, and residual tumor status did not differ between groups. In particular, residual tumor status was negative in 99% cases of the SPS group, and comparable to the recent randomized controlled trials (20,21). With regard to long-term oncological outcomes, Tei et al reported that the 3-year relapse-free survival rate and 3-year overall survival rate in the SPS group were 94.7 and 97.4%, over the median follow-up period of 40 months, respectively (7). The other four studies did not report for the long-term outcomes. The COLOR II Study Group reported that the 3-year relapse-free survival rate and 3-year overall survival rate in the laparoscopic surgery group were 74.8 and 86.7%, respectively (22). Jeong et al reported that the 3-year relapse-free survival rate and 3-year overall survival rate in the laparoscopic surgery group were 79.2 and 91.7%, respectively (23). The long-term outcomes of SPS for rectal cancer should be needed for further research.
This systematic review being compared the clinical outcomes between the SPS and MPS for rectal cancer has several important limitations. First, five studies composed of one randomized controlled study and four non-randomized studies with small number of patients, which were not the highest quality of evidence, were a limitation that might be affect the outcomes and induce selection bias, although the majority of the assessed outcomes across all papers had no dramatic conflicts in the findings. Second, there is a difference in terms of preoperative assessment, including tumor location (upper rectum, lower rectum, or distance from anal verge), clinical TNM classification and preoperative treatment. Third, there is a possibility that the results may be influenced by various surgical techniques and devices in the SPS group. Fourth, the long-term oncological outcome is controversial because of insufficient follow-up period after surgery.
This study confirmed the safety and feasibility of SPS for rectal cancer, with slighter postoperative pain, lower conversion rate to open surgery, lower postoperative complication rate and satisfactory oncological clearance. In the future, more randomized controlled trials with a large number of cases are needed to demonstrate the clinical and prognostic impact of the SPS for rectal cancer.