Laparoscopic surgery for colorectal diseases was first reported by Jacobs et al.1 and Fowler and White2 in 1991 and was introduced in Japan by Watanabe et al. in 1992 for early-stage colorectal cancer.3 This surgery has spread widely since it was covered by insurance in 1996. According to the Japan Society for Endoscopic Surgery survey, endoscopic surgery accounted for 72.0% of colorectal cancer cases in 2015.4 More than 20 years have passed since the first laparoscopic colorectal resection was performed. Several large clinical trials comparing laparoscopic surgery with open surgery have been reported, mainly for colorectal cancer and meta-analyses have been conducted. The safety and long-term results of laparoscopic surgery for colon and rectosigmoid cancer are comparable to those of open surgery and there is a favorable consensus on its usefulness. In contrast, laparoscopic surgery for transverse colon and rectal cancer is considered technically challenging and is not included in many randomized controlled trials and therefore remains controversial. Use of laparoscopic surgery for colorectal diseases is expected to continue to expand in the future with the development of surgical techniques and more advanced equipment. As an academic society, we need to show where laparoscopic surgery stands. This guideline evaluates clinical questions of particular interest among the various colorectal diseases. In the case of malignant diseases such as colon and rectal cancer, focusing on the long-term prognosis and short-term outcomes is a natural step to take. Additionally, in the case of benign conditions, the affected patients' ages were also taken into consideration and postoperative quality of life and cosmetics were also included among the evaluation items. Laparoscopic surgery for colon cancer was not superior to open surgery in terms of long-term prognosis. However, although the operative time tends to be longer, the short-term outcomes such as postoperative hospital stay, blood loss, and wound-related events may exceed those of open abdominal surgery. Laparoscopic surgery is therefore recommended. Compared with open surgery, laparoscopic surgery for colon cancer showed no significant difference in long-term prognosis such as for recurrence-free survival rate and overall survival rate after surgery regardless of the cStage in five large randomized controlled trials, their systematic reviews, and the Cochrane Review's systematic review.1-12 A large randomized controlled trial in Japan for Stage II/III patients revealed no statistical noninferiority in the long-term outcome of laparoscopic surgery compared to open surgery. However, the long-term outcomes from laparoscopic surgery and open surgery are considered to be nearly equivalent, given their better outcomes compared to those in Western countries.13 Systematic reviews of transverse colon cancer and locally advanced cancer (pT4 cancer) also showed no significant differences in long-term prognoses of recurrence-free survival and overall survival.1, 2 Short-term postoperative mortality and reoperation rates were not significantly different in one systematic review involving transverse colon cancer or in several randomized controlled trials, including those in Japan.2, 13-20 While some reports showed no significant difference in postoperative complications, others reported lower rates in laparoscopic surgery, and a large randomized Japanese trial also found lower rates of wound-related complications and early postoperative complications.2, 11, 13, 15-22 The amount of blood loss was significantly lower in laparoscopic surgery,8, 13, 16-19, 21 and operative time tended to be significantly longer in laparoscopic surgery.2, 8, 11, 13, 16-21 Postoperative hospital stay was significantly shorter for laparoscopic surgery including transverse colon cancer and Stage IV palliative resection, in four systematic reviews and several randomized controlled trials including Japan.2, 11, 13, 15-22 More specifically, laparoscopic surgery showed superior short-term results compared to open surgery including an earlier start of the diet and a shorter hospital stay. However, in representative large-scale comparative studies such as the CLASICC and COLOR studies in Europe and the COST study in the United States, the conversion rates to open surgery were high (29%, 17%, and 21%, respectively), and the postoperative complication rate was higher, and the postoperative hospital stay was longer in cases with conversion than in those without conversion. Although the conversion rate to open surgery in Japan was low at 5.4%, it is recommended that laparoscopic surgery should be performed at a facility with adequate technology and a skilled surgical team. In recent years, laparoscopic surgery with a reduced number of ports such as single port or reduced port laparoscopic surgery has emerged and is becoming popular in contrast to standard laparoscopic surgery (multiport surgery). This single-port (reduced-port) laparoscopic surgery can be performed safely in a limited number of cases by skilled surgeons and may be an option for laparoscopic surgery. However, although presumed to be less invasive and more cosmetic than standard laparoscopic surgery, it has yet to show clear superiority in short-term and long-term outcomes.23, 24 Robotic surgery is not currently covered by insurance for colon cancer in Japan (as of April 2018). This robotic surgery can be performed safely in a limited number of cases by skilled surgeons. It may, therefore, serve as an option for laparoscopic surgery but it has yet to demonstrate clear superiority in short-term and long-term outcomes.25 This operative procedure is applicable to all colon and rectosigmoid cancers regardless of the cStage.1-13, 21 Complete mesocolic excision and D3 lymph node dissection are preferred as radical surgery for advanced cancer.26 Especially in transverse colon cancer, the anatomical characteristics (relationship with blood vessels and surrounding organs) make lymph node dissection technically challenging. The application of this operative procedure should therefore be carefully determined according to the surgeon's skill level. Based on the results of large overseas comparative trials and systematic reviews, the short-term results of laparoscopic surgery for cancers in the cecum, ascending colon, descending colon, sigmoid colon, and rectosigmoid are better than open surgery, and the noninferiority of laparoscopic surgery for long-term results was demonstrated.1-12, 14-16, 18-22 In a large Japanese comparative study for colon cancer patients with cStage II and III (excluding transverse and descending colon), the short-term results were better for laparoscopic surgery than for open surgery, with lower rates of wound-related complications and early postoperative complications. The conversion rate to open surgery was 5.4%, lower than in Western clinical trials. Although statistical noninferiority was not demonstrated, which may be due to the high survival rate, the long-term outcomes were considered comparable.13, 17 Therefore, laparoscopic surgery deserves recommendation for cStage 0–III cancers in the cecum, ascending colon, descending colon, sigmoid colon, and rectosigmoid. However, advanced techniques are required for lymph node dissection and vascular dissection when the tumor is located in the transverse colon or splenic flexure. The application of this operative procedure should therefore be carefully determined according to the surgeon's skill level. Laparoscopic surgery as a palliative resection for cStage IV is safe and has a better perioperative outcome than open surgery, but the long-term outcome depends on subsequent medical treatment.22 Although a systematic review of laparoscopic surgery for locally advanced cancer (pT4) reported a higher conversion rate to open surgery (18.6%) and a 2.26 reduction in the number of lymph nodes dissected, the long-term prognosis was similar,1 the applications should therefore be determined according to the patient's condition and surgeon's skill level. In patients with coexisting severe respiratory or cardiovascular disease, the application of laparoscopic surgery should be carefully determined taking into account its significance. In patients with severe obesity or a history of laparotomy, its application should be determined according to the proficiency of the facility. Laparoscopic surgery affects respiratory and circulatory dynamics due to increased intra-abdominal pressure caused by carbon dioxide insufflation and intraoperative positional changes such as head-down and semi-supine positioning.27, 28 In particular, laparoscopic surgery should be carefully applied to patients with respiratory or cardiac diseases. It is necessary to decide on laparoscopic surgery while giving due consideration to intraoperative effects of carbon dioxide insufflation and repositioning during laparoscopic surgery on cardiopulmonary function and postoperative adverse events after laparotomy. Insufflation pressure should be kept low (14 mmHg or less, about 8 mmHg) while continuously monitoring the effects from carbon dioxide insufflation and gasless lift laparoscopic surgery might be considered. Risk factors such as advanced age, obesity, and a higher American Society of Anesthesiologists score are thought to be associated with mortality and complication rates after colorectal resection surgery. However, a report suggests that laparoscopic surgery is more effective than open surgery in high-risk cases.29 In this study, laparoscopic surgery was compared with open surgery in elderly, obese, and high-risk patients with comorbidities (anemia, congestive heart failure, valvular disease, chronic respiratory disease, liver disease, kidney disease, diabetes mellitus, etc.), and the results showed that laparoscopy had better short-term results and fewer complications. In any case, in cases with coexisting respiratory or circulatory disease, it is essential to evaluate the risk of intraoperative and postoperative complications in collaboration with anesthesiology and other departments and carefully determine the applications of laparoscopic surgery, while also considering the significance of the procedure. Although the conversion rate to open surgery is higher in obese patients, and the postoperative complication rate is also higher than that of nonobese patients, the long-term prognosis is similar to that for nonobese patients.30 Although there are reports that laparoscopic surgery after emergency laparoscopy or metallic stent insertion in obstructive colorectal cancer is not inferior to open surgery in terms of short-term and long-term outcomes,4, 31 the applications of these procedures should be determined according to the proficiency level of each facility and the experience of the surgeon. Although the short-term results of laparoscopic surgery are considered better and safer than those of open surgery, and the long-term results are comparable in elderly patients, the application of laparoscopic surgery should be carefully determined considering the general conditions and comorbidities of elderly patients. Many reports show the usefulness of laparoscopic surgery for the elderly. Even in patients over 80 years of age, laparoscopic surgery required a longer operation time than open surgery, resulting in less blood loss and a lower rate of postoperative complications.22 Some reports have shown no difference in surgical and short-term outcomes in age-specific studies.14 In Japan, a large-scale retrospective study of laparoscopic surgery versus laparotomy was conducted in patients aged 80 years or older.32 The results showed that laparoscopic surgery required a longer operative time than open surgery. Still, it resulted in less blood loss, and less postoperative hospital stay and postoperative complications were better for laparoscopic surgery. As for long-term results, it showed no difference in 3-year recurrence-free survival and 3-year overall survival. However, elderly patients often exhibit functional impairment of multiple organs, including respiratory and circulatory disorders, decreased reserve capacity, and mental disorders. The incidence of postoperative complications is expected to be higher than that in nonelderly patients. Careful perioperative management is therefore essential even in minimally invasive laparoscopic surgery. Committee voting results Laparoscopic surgery for rectal cancer may be superior to open surgery in terms of short-term outcomes such as postoperative hospital stay and blood loss compared to open surgery. In addition, previous reports have shown no difference in long-term prognosis. However, recent reports suggest that the quality of surgery may be inferior and the results of those trials need to be verified regarding the long-term prognosis. Compared with open surgery, laparoscopic surgery for rectal cancer showed no significant difference in long-term outcomes such as postoperative overall survival and recurrence-free survival in previous reports and meta-analyses.1-8 However, in 2017, the pathological findings showed that laparoscopic surgery was significantly inferior to laparotomy in surgical curability.9-11 The long-term prognosis of these clinical trials has not yet been reported, and the results will be of interest. The short-term postoperative results indicated no significant differences in short-term postoperative mortality or reoperation rates.5-10, 12-15 In an early clinical trial, the postoperative complications with laparoscopic surgery were reported to be inferior.12 However, subsequent reports showed either no significant difference or a lower rate in laparoscopic surgery.5-10, 12-15 In addition, the postoperative hospital stay was significantly shorter with laparoscopic surgery.5-10, 12-15 The amount of blood loss was significantly lower in laparoscopic surgery, but the results for operative time differed depending on the year of publication or the authors.5-10, 12-15 Committee voting results Laparoscopic surgery is recommended for acute appendicitis because it reduces the incidence of postoperative complications such as wound infection and intestinal obstruction, shortens postoperative hospital stay, and shows similar mortality and blood loss to open surgery, while increasing operative time. Three recent meta-analyses have shown that laparoscopic surgery for acute appendicitis increased the operative time compared with open surgery,1-4 but indicated similar mortality4 and blood loss,1 and reduced the postoperative complications and hospital stay.2, 4-6 Several meta-analyses showed a decrease in wound infection2, 7 and intestinal obstruction.5, 6 A meta-analysis reported a similar intra-abdominal abscess,2 but another reported decreased incidence.5 According to a recent randomized controlled trial, laparoscopic surgery for complicated appendicitis did not increase postoperative complications or reoperation rates compared with open surgery with a similar operative time.8 In addition, two meta-analyses showed that the incidence of intra-abdominal abscesses was similar and that the surgical site infection and postoperative hospital stay were reduced.9, 10 Recent meta-analyses and systematic reviews on laparoscopic surgery for obese patients with appendicitis have shown that laparoscopic surgery reduced the postoperative complications, wound infection, and postoperative hospital stay but with a variable (i.e., increased, decreased, or comparable) operative time compared to open surgery.11-13 Laparoscopic surgery for appendicitis in children reduced the postoperative complications, wound infection, and intestinal obstruction, although it increased the operative time compared with open surgery according to recent meta-analyses.2, 14, 15 In addition, one meta-analysis revealed an increase in intra-abdominal abscesses14 from laparoscopic surgery, and two meta-analyses revealed an equivalence.2, 16 Laparoscopic surgery for appendicitis patients aged 60 years or older reduced the postoperative hospital stay compared with open surgery with similar postoperative complications and operative time.17 The abortion rate in pregnant women with laparoscopic surgery for appendicitis was significantly higher than that with open appendicectomy,18 with a reported rate of 6%.19 However, the rate of premature deliveries was similar.18, 19 In meta-analyses of the single and three-port laparoscopic procedures for appendicitis patients, single-port laparoscopic surgery increased the operative time.20-22 Still, the results were more cosmetically pleasing,22 with similar postoperative complications and length of hospital stay.20-22 In addition, while many reports suggest that postoperative pain was similar,21-23 there was a report of increased postoperative pain.20 Committee voting results Laparoscopic surgery for diverticula of the large intestine is recommended because it is likely to have better short-term outcomes than open surgery in terms of postoperative pain, complications, length of hospital stay, and cosmetic appearance if the technique and experience of the facility and surgical team are considered adequate. Many reports1-3 indicated that laparoscopic surgery for diverticulitis prolonged the operative time compared to open surgery, but another4 reported similar times. In addition, many reports noted that laparoscopic surgery reduced the postoperative pain compared to open surgery,1, 5 allowed patients to start eating earlier,4 and shortened the postoperative hospital stay and time to return to society.2-4, 6 However, some prospective randomized trials reported no difference in short-term results between laparoscopic and open surgery.3 The total cost of medical care was also reported to be lower.1 Although a report1 has shown no difference in the incidence of postoperative complications, many reports3, 5, 6 have shown that laparoscopic surgery reduced postoperative complications. In particular, a decrease in the frequency of wound infection and ileus has been reported.2, 3, 6 The number of diverticulitis episodes was also reported as not a decisive factor in the decision on conversion to open surgery but rather the surgeon's experience with the procedure.7 Therefore, the short-term results are likely to be superior with laparoscopic surgery if the surgical team's proficiency level is high. However, a prospective randomized trial has reported no difference between laparoscopic and open surgery.1 Laparoscopic surgery for the diverticulitis of the large intestine with complications was reported to require a longer operative time but shorter postoperative hospitalization than open surgery.8 In the case of perforated diverticulitis (Hinchey Classification 3: panperitonitis with purulent ascites), laparoscopic lavage and drainage without intestinal resection had a higher efficacy rate, fewer complications, and lower mortality than conventional open resection of the diverticulitis portion of the intestine and colostomy (Hartmann surgery).9, 10 A systematic review also reported a less than 5% mortality rate, and most patients did not undergo colostomy.11 A subsequent multicenter randomized controlled trial12 showed no difference in mortality or serious complications. In addition, the laparoscopic group was effective with a shorter overall hospital stay and lower rates of reoperation and final colostomy. Although the efficacy of laparoscopic lavage has been demonstrated to result in fewer reoperations and shorter hospital stays in a randomized controlled trial in Sweden,13 two randomized controlled trials comparing with open resection of the lesion14, 15 found no benefit in laparoscopic lavage with no significant difference in serious complications and mortality. However, the follow-up has shown that laparoscopic surgery reduced medical costs more than open surgery.16 Another report has shown that a reduction in related costs was observed with laparoscopic lavage and drainage.17 In conclusion, laparoscopic lavage and drainage without intestinal resection may be an effective treatment option for perforated diverticulitis. There are no reports indicating a difference in early postoperative mortality between laparotomy and laparoscopic surgery in any stage of diverticulitis.3, 16, 17 Committee voting results Laparoscopic surgery for ulcerative colitis was not superior to open surgery in postoperative mortality. Still, it may be superior to open surgery in terms of postoperative quality of life, complications, length of hospital stay, and cosmetics and is therefore recommended. Surgical treatment for ulcerative colitis involves various patient backgrounds, disease states, and a wide range of operative procedures. Consequently, the severity of ulcerative colitis for which surgery is indicated varies, ranging from patients in generally a poor condition with toxic megacolon, perforation, or massive bleeding, for whom an emergency surgery is suggested, to relatively stable patients who can undergo elective surgery. In addition, because surgery is often performed on relatively young patients and it is necessary to consider surgical procedures by taking into account their long life after surgery, this guideline emphasizes the outcome of postoperative quality of life in addition to short-term postoperative mortality and postoperative complications. In regards to short-term postoperative mortality in laparoscopic surgery for ulcerative colitis compared with that in open surgery, the outcome was zero to very rare in one randomized controlled trial1 and nine observational studies2-10 with no significant difference. On the other hand, an observational study on the postoperative results of elective total colectomy showed that the short-term postoperative mortality rate was significantly higher for open surgery compared with laparoscopic surgery. However, it should be noted that ulcerative colitis accounts for about 30% of the cases, and other diseases such as colorectal cancer and Crohn's disease were also included.11 No differences in postoperative quality of life were observed in two randomized controlled trials1, 12 and 10 observational studies.3-5, 10, 13-18 Two observational studies19, 20 showed significantly less use of postoperative analgesics in laparoscopic surgery. Regarding postoperative complications, there have been one randomized controlled trial1 and 23 observational studies,2-11, 13, 14, 17-27 and many reports have reported no difference or fewer complications with laparoscopic surgery. Some reports have shown that wound-related complications, adhesions, and intestinal obstruction were significantly less common with laparoscopic surgery.2, 7, 9, 10, 27 No differences in postoperative reoperation rates were observed in any of five observational studies.7-9, 21, 23 Laparoscopic surgery was superior in terms of cosmetics, postoperative hospital stay, and blood loss,3, 5, 7, 8, 10-15, 19, 23, 24, 28 while the operative time was significantly longer in laparoscopic surgery.1, 3, 6, 7, 13, 14, 17, 19, 20, 23-25, 29 No difference in cost was observed in one randomized controlled trial.1 Two observational studies on pediatric patients found that wound-related complications and postoperative intestinal obstruction were less common with laparoscopic surgery.21, 25 There are six observational studies on severe cases and emergency surgery cases.8, 9, 14, 19, 23, 24 Most of these reported no difference or fewer postoperative complications with laparoscopic surgery and fewer postoperative hospital days with laparoscopic surgery. However, all of these are observational studies and the level of evidence is low. Committee voting results Laparoscopic surgery for Crohn's disease is not superior to open surgery in postoperative endoscopic and surgical recurrence rates. Laparoscopic surgery is also not expected to change the long-term prognosis of Crohn's disease. Still, it may exceed open surgery in short-term outcomes such as postoperative complications, length of hospital stay, and cosmetics. Laparoscopic surgery is therefore recommended for Crohn's disease. There are two randomized controlled trials on laparoscopic surgery for Crohn's disease,1, 2 which included only ileal resection. Although ileal resection is the most common surgery for Crohn's disease, a wide variety of surgeries are actually performed including partial resection of the small intestine, stricturoplasty, large intestinal surgery, including total colectomy and subtotal proctocolectomy, and surgery for the formation of fistula such as internal or external fistula. It is therefore not clear whether the results from randomized controlled trials can be applied to Crohn's disease surgery as a whole. Therefore, reducing the rating down by one level was considered for the level of evidence. In regard to short-term postoperative mortality rate, a study using data from 443 950 patients in the Nationwide Inpatient Sample Database in the United States reported that mortality rate was three times higher in open surgery than in laparoscopic surgery.3 On the other hand, no deaths were observed in the two randomized controlled trials.1, 2 Short-term postoperative complications were significantly lower in laparoscopic surgery than in open surgery in both of the two randomized controlled trials.1, 2 In addition, the study mentioned above on a large population using the Nationwide Inpatient Sample database also showed a significantly lower rate for complications with laparoscopic surgery.3 The endoscopic recurrence rate of Crohn's disease was similar for both laparoscopic and open surgery in both observational studies of short-term results within 1 year after surgery4 and a study of long-term results over a mean observation period of 10 years after a randomized controlled trial.5 In addition, the two randomized controlled trials showed no difference between laparoscopic and open surgery in reoperation rates related to Crohn's disease recurrence,1, 2 and most of the systematic reviews and new comparative studies reported no difference.6-9 Postoperative quality of life in the randomized controlled trials was comparable in the short term (within 3 months after surgery) and the long term (6.7 years [median]) postoperative observation period.2, 10 In terms of cosmetics, a randomized controlled trial showed laparoscopic surgery resulted in significantly shorter wounds1 and better body image and cosmesis scores over the long term.10 Two randomized controlled trials, several systematic reviews, and several new comparative trials showed that operative time was significantly longer with open surgery1, 2, 7-9, 11, 12 and that postoperative hospital stay was significantly shorter with laparoscopic surgery.1, 2, 7-9, 11-15 Bleeding volumes were comparable.1, 8, 11, 12 Committee voting results Japan has an aging population, and an increasing number of elderly patients have colorectal cancer. Although laparoscopic surgery is expected to benefit elderly patients because it applies less of a physical burden, clinical trials often exclude elderly patients from the eligibility criteria and there is not much evidence on colorectal cancer in the elderly. However, several observational studies have demonstrated the usefulness of laparoscopic surgery. In an observational study in Japan, 1526 cases of colon cancer and 282 cases of rectal cancer in patients aged 80 years or older were collected. The analysis after propensity score matching showed that postoperative complications were less common after laparoscopic surgery for colon cancer.1 A systematic review of observational studies of patients aged 85 years and older similarly showed a trend toward fewer complications and shorter hospital stays with laparoscopic surgery.2 A randomized controlled study of 200 patients aged 75 years or older reported that laparoscopic surgery showed fewer complications and less blood loss in the short term with a similar mid-term prognosis compared to open surgery.3, 4 In a comparison of laparoscopic surgery between younger and older patients, a systematic review of patients aged 75 years or older and those younger than 75 years concluded that although complications were slightly more common in older patients, there was no increase in anastomotic leakage or mortality and that the procedure was generally performed safely.5 Progress made in minimally invasive endoscopic surgery has made surgery using surgical-assist robots (from here onwards referred to as "robotic surgery") widespread in Japan in recent years, and robotic surgery for prostate cancer in the field of urology has been covered by insurance since April 2012. Robotic surgery has also been approved for rectal surgery in the colorectal field since April 2018. Although tactile sensation is inferior to open or laparoscopic surgery, the robot's multiarticulated forceps, image stabilization function, and stable three-dimensional high-definition images are expected to achieve more accurate and delicate surgery during rectal surgery that requires complicated surgery within the narrow pelvis.1-3 However, there is currently insufficient evidence to demonstrate the superiority of robotic surgery over laparoscopic surgery. The only large randomized controlled trial comparing robotic versus laparoscopic surgery (the ROLARR trial) found no significant difference in the primary outcome, the rate of conversion to open surgery. Furthermore, no results exceeded those obtained with laparoscopic surgery in secondary outcomes such as complications, and pathological, oncological, and functional outcomes.4 Although meta-analyses often reported that robotic surgery had a lower conversion rate to open surgery,5-15 longer operative time,5-8 and comparable postoperative and oncological outcomes,6, 9-13 it is essential to note that the majority of included studies are observational. Several observational studies have shown that the long-term prognosis after robotic surgery was comparable to that of laparoscopic surgery.16, 17 The evidence for robotic surgery for colon surgery is limited. However, in a Korean randomized controlled trial, robotic surgery was associated with longer operative time and higher costs than laparoscopic surgery without contributing to oncological outcomes such as recurrence or survival, or postoperative recovery.16 Robotic surgery in the colorectal field is still in its infancy. The results are comparable to those of laparoscopic surgery in observational studies, but further advances are expected, including a shorter operative time with learning curves, cost reductions through the development of new devices, and additional weight savings. In regard to the development and dissemination of robotic surgery, it is necessary to discuss the accumulation of technology and experience, establishment of larger scale and higher quality evidence, the medical and economic aspects, and enhancement of certification systems and educational programs, and so forth. Laparotomy is considered difficult for obese patients with colorectal cancer, resulting in longer operative time and more complications, and laparoscopy is expected to offer the advantage of less abdominal wall destruction. However, laparoscopy also requires use of more advanced techniques than usual due to difficulty in securing the field of view. The definition of obesity is generally body mass index (BMI) >25 in Asia, including Japan, and BMI >30 in the West. It has long been reported that laparoscopic surgery in obese patients with colorectal cancer results in prolonged operative time and increased postoperative complications compared to the nonobese group,1 and a recent systematic review reported a significantly higher conversion rate to open surgery, postoperative complications, wound infection, and anastomotic leakage.2 On the other hand, there was no apparent difference in the number of lymph nodes dissected, the surgical margins, and long-term prognosis.2, 3 However, it should be noted that all of these reviews are based on results from observational studies. Therefore, in colorectal cancer patients with obesity, the application of laparoscopic surgery must be determined while bearing in mind the possibility of a poor short-term prognosis. There are no reports of randomized controlled trials of laparoscopic surgery versus open surgery in obesity. However, a subgroup analysis of overall survival in the JCOG0404 randomized controlled trial (noninferiority trial) comparing laparoscopic surgery and open surgery in patients with cStage II–III colorectal cancer conducted in Japan showed that the prognosis of obese patients with BMI >25 in laparoscopic surgery was worse than that in open surgery.4 However, this is also only a subgroup analysis, so care should be taken in interpreting the results. It must be verified by further clinical trials. Furthermore, there are reports that newer approaches such as robotic surgery and transanal approaches (TaTME) are more effective than laparoscopic surgery for obese patients with rectal cancer.5, 6 There is still a lack of evidence on how to approach colorectal cancer with obesity, and further development of high-quality evidence is needed. Laparoscopic surgery for Stage IV colorectal cancer is expected to offer the advantages of less invasive and early chemotherapy in the case of palliative resections and of continued liver and lung surgery in the case of curative treatment. Still, there are concerns that it may be inadequate treatment compared to open surgery. In addition, the size and invasion of the tumor make laparoscopic surgery difficult and the conversion rate to open surgery can be high. Although the results of a large randomized controlled trial for Stage IV colorectal cancer have not been reported to date, based on results from an observational study, the JCOG is currently conducting a randomized controlled trial on the efficacy of laparoscopic surgery for primary tumor resections in advanced unresectable colorectal cancer.1 Observational studies and meta-analyses of nonradical resection of primary lesions have shown that laparoscopic surgery required a longer operative time but less blood loss than open surgery, had better short-term outcomes such as postoperative complications, and required fewer postoperative hospitalization days. However, there was no significant difference in long-term results.2, 3 Similar results have been reported for symptomatic Stage IV colorectal cancer.4 The evidence level for laparoscopic surgery for resectable lesions is low, although the usefulness of laparoscopic surgery has been reported for both primary lesions and metastatic lesions. Although there is no consensus on whether or not to resect the primary lesion in patients with Stage IV colorectal cancer that cannot be radically resected, results from randomized controlled trials have not yet confirmed the usefulness of laparoscopic surgery. However, the short-term results appear promising and laparoscopic surgery may therefore at present serve as a treatment option. Data sharing is not applicable to this article as no new data were created or analyzed in this study. Yoshiyuki Ishii received grant to his institution for another work from Chugai Pharmaceutical Co., Ltd. Koya Hida received lecture fee from Olympus Corporation, Intuitive Corporation, Johnson and Johnson and Medtronic. The other authors declare that they have no conflicts of interest to disclose.
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