Patient populations and surgeons
Consecutive patients who underwent laparoscopic surgery (including MPLS and SILS) for DCC between April 2008 and December 2018 at Osaka Police Hospital and Osaka Rosai Hospital were assessed. Cases of obstruction or perforation that required emergent operation were excluded from this study.
The first case of SILS for DCC was carried out in March 2011. Since then, the indications for SILS have gradually been expanded to include advanced cancers. Patients received a sheet describing the differences between MPLS and SILS, and also received a thorough explanation of each operative procedure. All patients agreed to undergo SILS, and provided written informed consent.
Surgical procedures for DCC according to the tumor location
According to the Japanese Society for Cancer of the Colon and Rectum Guideline for the Treatment of Colorectal Cancer [11], D2 lymph node dissection was performed for clinical T1 tumor and D3 lymph node dissection for clinical T2 or greater tumors. In principle, at least 10 cm of normal bowel both proximal and distal to the tumor was resected. For patients with tumor located in the proximal one-third of the descending colon [12,13], we performed left hemicolectomy with D3 lymphadenectomy, which involves complete dissection of the pericolic lymph nodes (node station 221, 231, and 241), intermediate lymph nodes (nodes 222, 232, 242, and 252), main lymph nodes (node 223) along the middle colic artery (MCA), and main lymph nodes (node 253) along the inferior mesenteric artery (IMA) as defined by the Japanese Society for Cancer of the Colon and Rectum [14]. On the other hand, segmental colectomy was performed for DCC located in the distal two-thirds of the descending colon [12,13]. In segmental colectomy, D3 lymphadenectomy involves complete dissection of regional lymph nodes, including the pericolic lymph nodes (nodes 221, 231, and 241), intermediate lymph nodes (nodes 232, 242, and 252), and main lymph nodes (node 253) along the IMA as defined by the Japanese Society for Cancer of the Colon and Rectum [14].
Data collection
Patient age, sex, body mass index (BMI), Eastern Cooperative Oncology Group performance status (ECOG-PS), American Society of Anesthesiologists (ASA) score, previous abdominal surgery, clinical TNM classification, and comorbidities were obtained from the medical records. As listed in Table 1, cardiac disease consisted of ischemic disease, chronic heart failure or cardiomyopathy. Pulmonary disease consisted of asthma, chronic obstructive pulmonary disease or interstitial pneumonia. Cerebrovascular disease consisted of a history of transient ischemic attacks or cerebrovascular events with or without neurological deficit. Postoperative complications were classified according to the Clavien-Dindo classification [15]. Infectious complications consisted of abscess, colitis, urinary tract infection, nephritis, catheter-related infection, or cholecystitis. Operative mortality was defined as death during the same admission or within 30 days of surgery. All patients were followed-up for at least 30 days after surgery. This study was approved by the institutional review boards at Osaka Police Hospital (approval number 1468) and Osaka Rosai Hospital (approval number 2021-82).
Statistical methods
Prior to propensity score-matching, the t test or Wilcoxon rank-sum test was used for continuous variables, and the χ2 test or Fisher’s exact test was applied for categorical variables. Propensity score-matching was then applied to minimize the possibility of selection bias and to adjust for significant differences in the baseline characteristics of patients (Fig. 1). The first step in the matching process was to complete a multivariate logistic regression analysis to obtain propensity scores. The following 9 covariates that might affect short- and long-term outcomes for SILS were included in the model for calculating the propensity score: age, sex, ECOG-PS, ASA score, previous abdominal surgery, and clinical TNM classification. The next step was the 1:1 matching process, using calipers set at 0.2. This propensity score-matching was used to evaluate the effects of SILS on surgical and pathological outcomes. After propensity score-matching, baseline characteristics, including covariates not entered into the propensity score model, were compared between groups using bivariate analyses.
Data are presented as the median and interquartile range (IQR) for continuous variables and as the frequency and percentage for categorical variables. The c2 test was used for comparisons of categorical variables. Student’s t test was used to determine the significance of differences between continuous variables. Survival curves were calculated using the Kaplan-Meier method and were then compared by log-rank testing. Values of p<0.05 were considered statistically significant. All statistical analyses were performed using JMP version 16.0 software (SAS Institute, Cary, NC, USA).