Profilin 2 isoform expression is associated with lung metastasis of colorectal cancer according to a comprehensive gene expression study using a mouse model.

Lung metastasis is the second most common type of metastasis in colorectal cancer. Specific treatments for lung metastasis have not been developed since the underlying mechanisms are poorly understood. The present study aimed to elucidate the molecular basis of lung metastasis in colorectal cancer. In a mouse model, cell lines that were highly metastatic to the lungs were established by injecting colorectal cancer cells through the tail vein and removing them from the lungs. Differential gene expression comparing the transfected cells with their parental cells was investigated using DNA microarrays. The results were functionally interpreted using gene enrichment analysis and validated using reverse transcription-quantitative PCR (RT-qPCR). The isoforms of the identified genes were examined by melting curve analysis. The present study established colorectal cancer cell lines that were highly metastatic to the lungs. DNA microarray experiments revealed that genes (N-cadherin, VE-cadherin, Six4, Akt and VCAM1) involved in motility, proliferation and adhesion were upregulated, and genes (tissue inhibitor of metalloproteinase-3 and PAX6) with tumor-suppressive functions were downregulated in metastatic cells. Profilin 2 (PFN2) expression was upregulated in multiple metastatic cell lines using RT-qPCR. Two PFN2 isoforms were overexpressed in metastatic cells. In vitro and in vivo models were established and genes associated with lung metastasis were identified to overcome the heterogeneity of the disease. Overall, aberrant PFN2 expression is unreported in lung metastasis in colorectal cancer. In the present study, two PFN2 isoforms with differential tissue distribution were upregulated in metastatic cells, suggesting that they promote lung metastasis in colorectal cancer.

The impact of preclinical clerkship in general surgery on medical students' attitude to a surgical career.

PURPOSE: With the advent of a new program for postgraduate medical students in 2004, the number of applicants choosing surgical careers in Japan has been declining. We conducted this study to evaluate the impact of preclinical clerkship and how it affects students' attitudes toward a surgical career. METHODS: The subjects of our study were fifth-year medical students who participated in a clinical clerkship in general surgery in our department between April 2021 and March 2022. We conducted pre- and post-preclinical clerkship surveys to assess the perceived image of surgeons and the impact of clerkship on surgical career interest. RESULTS: Among 132 medical students (77 men and 55 women) who rotated through preclinical clerkship in our department, 125 participated in the survey and 66% expressed interest in a surgical career. In the post-clerkship survey, an increased interest in a surgical career was expressed by 79% of the students; notably, including those who initially expressed interest. Approximately 77% of students were satisfied with the practical skill training they received. CONCLUSION: Engaging medical students early in surgical experience through a preclinical clerkship for general surgery appears to promote their interest in a surgical career.

Relationship between obesity-related colorectal tumors and the intestinal microbiome: an animal-based trial.

PURPOSE: Obesity is a risk factor for colorectal cancer (CRC), and the intestinal microbiome is considered to contribute to CRC and obesity. Nonetheless, the role of the intestinal microbiome in obesity-related CRC is unclear. This study aimed to clarify the relationship between obesity-related CRC and the intestinal microbiome using a mouse model. METHODS: We compared an obese and insulin-resistant type 2 diabetes mouse model [KKAy] to wild-type mice (WT) [C57BL/6 J]. Azoxymethane was intraperitoneally injected to develop a mouse model CRC. At 26 weeks, we compared the number of tumors and the intestinal microbiome. We also compared them across two models, namely, antibiotic cocktail and co-housing. RESULTS: In all models, KKAy mice had a significantly greater number of tumors than WT mice. Analysis showed that the distribution of the intestinal microbiome changed in both models; however, no difference in tumor development was observed. Tumor expression was suppressed only in the antibiotic cocktail model of WT, whereas KKAy mice bore tumors (C57Bl/6 J: KKAy, 0/9:8/8; p < 0.001). KKAy mice remained predominantly tumor-bearing in all treatments. CONCLUSION: Based on the results, the intestinal microbiome may not be associated with tumorigenesis in obesity-related CRC. It may be necessary to think of other facts linked to obesity-related CRC.

Role of EphB2/ephrin-B1 signalling in the development and progression of obesity-associated colorectal cancer.

Obesity is a major problem worldwide and has been associated with colorectal cancer development, among other diseases. Ephrin receptors and ligands play an important role in the turnover of the intestinal mucosa and intestinal crypt compartmentalization. It has been hypothesised that obesity-induced inflammation affects ephrin signals, leading to carcinogenesis. Therefore, the aim of the present study was to assess the relationship between Eph-ephrin B signalling, obesity and obesity-associated colorectal cancer. An azoxymethane-induced obesity-associated cancer KKAy mouse model developed in our prior study was used. A total of 46 patients with consecutive colorectal cancer and 48 tumours were analysed. Immunohistological analyses were performed in mouse and human samples, and immunoreactive scores (IRS) were determined. KKAy mice were significantly more prone to cancer development compared with control C57/BL mice (2/15 in C57/BL vs. 10/10 in KKAy; P<0.001). TUNEL assay revealed a lower number of apoptotic cells in normal mucosa of KKAy mice (8.8% in C57/BL vs. 3.2% in KKAy; P<0.001) and obese patients (9.2% with BMI <25 vs. 3.6% with BMI ≥25; P=0.021). Immunohistological analysis revealed that ephrin-B1 was downregulated in normal mucosa from KKAy mice and obese patients (IRS, 2.86 with BMI <25 vs. 6.00 with BMI ≥25; P=0.002). Moreover, EphB2 was downregulated in tumours from KKAy mice and obese patients (IRS, 6.58 with BMI <25 vs. 3.83 with BMI ≥25; P<0.001). The distribution of infiltrated macrophages corresponded to the MCP-1 expression pattern in KKAy mice, and the number of macrophages was also significantly higher in those mice (36.3 in C57/BL vs. 120.0 in KKAy; P=0.029). The findings suggested that obesity results in disruption of EphB2/ephrin-B1 signalling, promoting colorectal cancer development and progression.

Metformin inhibits the development and metastasis of colorectal cancer.

Metformin is a commonly used drug for the treatment of diabetes. Accumulating evidence suggests that it exerts anti-cancer effects in many cancers, including colorectal cancer. However, the underlying molecular mechanisms of colorectal cancer metastasis remain unclear. Colorectal cancer cell lines were treated with metformin, and cell proliferation, invasion, and migration were analyzed in vitro. The relationship between metformin and the AMPK-mTOR axis was assessed by Western blot analysis and transfection with small interfering RNA. A colorectal cancer xenograft mouse model was used to observe the effects of metformin on liver metastasis. Immunohistochemical analysis was performed on liver metastatic tumors. In in vitro experiments, metformin significantly inhibited the proliferation, migration, and invasion only in HCT116 and SW837 cells, but not in HCT8 and Lovo cells. Only in HCT116 and SW837, a change in AMPK-mTOR expression was observed in a dose-dependent manner. In colorectal cancer xenograft mice, the liver metastatic rate (10% vs. 50%, p = 0.05) and the number of liver metastatic nodules (0.1/body vs. 1.2/body, p = 0.04) were significantly lower in the metformin group. Tumor proliferation and EMT were decreased and apoptosis was promoted only in metastatic liver tumors of mice treated with metformin. The molecular mechanism of the anti-cancer effects of metformin involves repression of mTOR pathways via AMPK activation. Moreover, the differences in metformin sensitivity depend on the response of the AMPK-mTOR pathway to metformin. Our study provides a theoretical basis for the anti-metastatic treatment of colorectal cancer using metformin.

Efficacy of side-to-end anastomosis to prevent anastomotic leakage after anterior resection for rectal cancer.

The present study aimed to investigate whether side-to-end anastomosis could provide an improved surgical outcome, such as lower anastomotic leakage rate, compared with end-to-end anastomosis, following anterior resection for rectal and rectosigmoid cancer. This retrospective study included 162 patients with rectal cancer who underwent elective anterior resection between January 2012 and October 2019 at a single institution. Patients with double cancers or colonic J-pouch were excluded. Anastomotic leakage was defined clinically and radiologically. Side-to-end anastomosis was introduced in the International University of Health and Welfare Mita Hospital in January 2017. Side-to-end anastomosis was performed in 63 patients, while end-to-end anastomosis was performed in 99 patients. Tumors tended to be located lower in the rectum in the side-to-end anastomosis group than in the end-to-end anastomosis group. No significant differences were observed in other patient characteristics. The incidence of anastomotic leakage was significantly lower in the side-to-end anastomosis group than in the end-to-end anastomosis group (3/63, 4.8% vs. 18/99, 18.2%, respectively, P=0.02). No significant differences were observed in the incidence rates of other complications. Univariate and multivariate analyses revealed that a smoking habit (P=0.04) and side-to-end anastomosis (P=0.02) were significantly associated with anastomotic leakage. In conclusion, side-to-end anastomosis using a double-stapling technique following anterior resection for rectal cancer may prevent anastomotic leakage.

Surgical glove perforation during laparoscopic colorectal procedures.

BACKGROUND: It has been reported that in conventional open surgery, approximately 10% of surgical gloves are perforated during surgery without being noticed. To protect both the patient and medical staff from harm, double gloving or changing gloves routinely at certain intervals during surgery is recommended. However, whether these protective measures are also necessary for laparoscopic colorectal surgery is unknown because the actual perforation rate during laparoscopic procedures is unclear. METHODS: Seventy-seven laparoscopic colorectal surgeries were evaluated, and a total of 616 surgical gloves used in the surgeries were collected for analysis. The presence of glove perforation was tested by the standard water-leak test method (EN455-1). RESULTS: Seven perforations were detected (1.1%). The duration of the laparoscopic procedure was not a statistically significant risk factor for glove perforation (p = 0.41). Postoperative surgical site infections (SSIs) were observed in 12 cases (15.6%), but there was no significant correlation between the presence of glove perforation and SSI (p = 0.92). According to the bacterial cultivation results, the majority of causative agents of SSI were enterobacteria, which belong to the major gut flora. CONCLUSION: Although the perforation rate was considerably lower than that in open surgery, surgical glove perforation occurred during laparoscopic procedures. Double gloving in laparoscopic colorectal surgery is recommended not to prevent SSI but to protect medical workers from harmful infections after direct contact with the patient.

Colectomy risk score predicts pouchitis in patients with ulcerative colitis.

Risk stratification is required to improve the management of pouchitis with ulcerative colitis (UC) patients who undergo ileal pouch-anal anastomosis (IPAA). Recently, the colectomy risk score (CRS) has been used to assess UC severity and predict the need for surgery. We explored whether the CRS predicted pouchitis in patients with UC who underwent IPAA. This retrospective study included 168 UC patients who underwent IPAA. Pouchitis was diagnosed according to the pouchitis disease activity index. The primary endpoint was the cumulative incidence of pouchitis. The risk factors for pouchitis using preoperatively obtained data, including the CRS, were investigated. Based on their CRS, patients were assigned to low- (scores 0-3), intermediate- (scores 4-6), and high-risk (scores 7-9) groups. The incidence of pouchitis was estimated using the Kaplan-Meier curve. CRS validity was assessed using the Cox proportional hazards model. During the median 7.2 (interquartile range [IQR] 2.8-11.1) years' follow-up, 37 (28.5%) patients were diagnosed with pouchitis. Patients with pouchitis had significantly higher CRS than patients without pouchitis (median 7.0; IQR, 4.0-7.0 vs median 5.0; IQR, 3.0-7.0). The cumulative incidences of pouchitis in the low-, intermediate-, and high-risk groups were 10.3%, 18.3%, and 36.1% at 5 years, respectively. Thus, the incidence trended to increase significantly as CRS increased. Multivariate analysis revealed high-risk CRS status was an independent predictor of pouchitis (hazard ratio: 18.03; 95% confidence interval 1.55-210.05). CRS is useful in risk stratification for the development of subsequent pouchitis in patients with UC undergoing IPAA.

Impact of intraoperative hypocapnia on postoperative complications in laparoscopic surgery for colorectal cancer.

PURPOSE: In laparoscopic surgery (LS) for colorectal cancer (CRC), the relationship between intraoperative end-tidal carbon dioxide concentration (EtCO2) and surgery-related complications remains unexplored. This study assessed the impact of intraoperative EtCO2 on postoperative complications in LS for CRC. METHODS: In total, 909 patients who underwent LS for CRC were enrolled. Hypocapnia and hypercapnia were defined as EtCO2 < 35 mmHg and > 40 mmHg, respectively, and the relationships between hypocapnia or hypercapnia duration and postoperative complications were analyzed. RESULTS: The median (range) durations of hypocapnia and hypercapnia were 2.0 (0-8.3) h and 0.3 (0-5.8) h, respectively. Complications were observed in 208 cases (23.0%), which included 37 (4.1%) instances of anastomotic leakage and 86 (9.5%) of superficial surgical site infection (SSI). While the hypercapnia duration was not associated with the short-term outcomes, prolonged hypocapnia was significantly correlated with complications (p = 0.02), specifically superficial SSI (p = 0.005). Multivariate analyses adjusted for confounding factors confirmed that hypocapnia prolongation was an independent risk factor for postoperative superficial SSI [OR 1.19; 95% confidence interval (Cl) 1.03-1.36, p = 0.01]. CONCLUSION: Intraoperative hypocapnia may be a risk factor for postoperative complications, in particular superficial SSI, in LS for CRC.

Evaluation of abdominal aortic calcification by plain CT predicts anastomotic leakage in laparoscopic surgery for colorectal cancer.

BACKGROUND: Anastomotic leakage is one of the most severe and critical complications of laparoscopic surgery for colorectal cancer. However, definitive preoperative predictors of anastomotic leakage remain elusive. With the ageing of society, the number of colorectal cancer patients with arteriosclerotic disease in Japan is increasing. This study was performed to evaluate the correlation between preoperative arteriosclerosis and anastomotic leakage. METHODS: In total, 98 patients undergoing laparoscopic surgery for colorectal cancer with reconstruction using the double-stapling technique without diversion of the stoma were enrolled in the study. Preoperative assessment of arteriosclerotic disease was performed by abdominal computed tomography. The calcification volume percentage of the aorta between the level of the celiac artery root and aortic bifurcation was calculated using ZIOstation2 software, and the relationship between arteriosclerosis and anastomotic leakage was analysed. RESULTS: Among 98 cases, anastomotic leakage was observed in 16 (16.3%). The median calcification volume percentage (range) was 2.35% (0-40.3%). Age, male sex, hypertension, dissection number, estimated glomerular filtration rate and tumour location were correlated with anastomotic leakage on statistical analysis. Statistical analysis showed that calcification volume percentage was one of the robust risk factors for anastomotic leakage (odds ratio: 1.09, 95% confidence interval: 1.03-1.17, P < 0.01). CONCLUSIONS: Calcification of the abdominal aorta may be a promising predictor of AL after laparoscopic surgery for colorectal cancer reconstruction using the double-stapling technique.

BAF57 Is a Potential Determinant of Colorectal Cancer Malignancy.

BACKGROUND/AIM: The role of brahma-related gene 1 (BRG1)-associated factor 57 (BAF57), a transcription factor, has been determined in prostate, breast, and ovarian cancer. However, the relationship between BAF57 and colorectal cancer (CRC) is obscure. Thus, we examined the functional correlation between BAF57 expression and oncological malignancy in CRC in vitro. MATERIALS AND METHODS: BAF57 expression in WiDr and HT29 CRC cell lines and clinical specimens from CRC patients was analysed by western blotting and/or RT-PCR. BAF57 expression was down-regulated in WiDr cells through siRNA transfection. An invasion assay was also performed to assess malignancy. RESULTS: BAF57 was expressed in both human CRC cell lines. Overall survival and recurrence-free survival rates were significantly reduced in high BAF57-expressing specimens. BAF57 expression was an independent predictive factor for long-term survival. CONCLUSION: BAF57 correlates with oncological malignancy and may be a novel therapeutic target in CRC.

Lymph node metastasis is strongly associated with lung metastasis as the first recurrence site in colorectal cancer.

BACKGROUND: The lymphatic system is known to be the primary pathway of metastasis for colorectal cancer. However, beyond regional lymph node metastases, little is known about the pathway of lymphatic metastases and the differences in the recurrence site risk. The aim of this study was to clarify the relationship between lymph node metastasis and the first recurrence site in colorectal cancer. METHODS: Patients with colorectal cancer who underwent curative resection in our institution between January 2003 and December 2016 were included in this analysis. The relationship between the first recurrence site and clinicopathological factors was analyzed by the Cox regression model and competing risk regression model. RESULTS: In total, 1,249 patients with colorectal cancer were included in this analysis. We found that the stages of lymph node metastases (N0 vs N1: P = .008, N0 vs N2a: P < .001, N0 vs N2b: P < .001) were significantly associated with lung metastasis in the multivariate analysis. Furthermore, in the competing risk analysis, the stages of lymph node metastases were significantly correlated with lung metastasis (N0 vs N1: P = .002, N0 vs N2a: P < .001, N0 vs N2b: P < .001) but were not correlated with other recurrence sites. CONCLUSION: The severity of lymph node involvement had a strong correlation with lung metastases in patients with colorectal cancer.

Inhibition of Heat-shock Protein 27 Reduces 5-Fluorouracil-acquired Resistance in Human Colon Cancer Cells.

BACKGROUND/AIM: In previous work we showed that expression of heat-shock protein 27 (HSP27; encoded by HSPB1) was associated with inherent resistance to 5-fluorouracil (5-FU). However, the relationship between HSP27 and acquired resistance remains unknown. MATERIALS AND METHODS: We generated an acquired resistance model (WiDr-R) of a colon cancer cell line by exposing WiDr cells to 5-FU. Cell viability assays under treatment with 5-FU, as well as down-regulation of HSP27 using small interfering HSP27 RNA, were performed. HSP27 mRNA and protein expression was analyzed using real-time polymerase chain reaction and western blotting. RESULTS: 5-FU-acquired resistance induced overexpression of HSP27 mRNA and protein levels in WiDr-R cells. Furthermore, siRNA knockdown of HSP27 in WiDr-R cells reduced 5-FU-acquired resistance. CONCLUSION: These findings demonstrate that HSP27 is associated with 5-FU resistance in human colon cancer cell cells and suggest that HSP27 regulation represents a novel approach to overcoming chemoresistance in colorectal cancer.

Horizontal spread of pericolic lymph node metastasis as a prognostic factor for recurrence in Stage III colorectal cancer.

AIM: Main lymph node (LN) metastasis dissected with a high vascular tie at the root of the feeding artery is a poor prognostic factor in colorectal cancer (CRC). However, the effects of horizontal spread on recurrence after curative resection remain unclear. The purpose of this study is to evaluate the relationship between the horizontal spread of LN metastasis and recurrence in CRC. METHOD: In this retrospective study, 189 CRC patients (98 men, 91 women) who underwent curative resection at our hospital from 2003 to 2018 and had only pericolic LN metastasis were divided into two groups: patients with LN metastasis beside the tumour only (T group, n = 121) and those with LN metastasis with horizontal spread (S group, n = 68) (mean follow-up period 50.9 ± 34.1 months). The primary outcome was recurrence-free survival (RFS). We investigated the correlation between clinicopathological background factors and recurrence using Cox regression analysis. RESULTS: Fewer than three LN metastases (N1) were found in 157 patients (107 T group, 50 S group), and four or more metastases (N2a) were found in 32 patients (14 T group, 18 S group). Univariate analyses revealed significantly shorter RFS in the S group [hazard ratio (HR) 1.95, 95% CI 1.07-3.55; p = 0.03). Multivariate analyses revealed that horizontal spread is an independent risk factor for recurrence (HR 1.95, 95% CI 1.05-3.68; p = 0.03). CONCLUSION: Although further investigation is needed, horizontal spread of LN metastasis is a prognostic factor for recurrence in Stage III CRC.

The Impact of Smoking on Pulmonary Metastasis in Colorectal Cancer.

INTRODUCTION: Recently, clinical studies have revealed that smoking can contribute to the poor prognosis of colorectal cancer (CRC) and, additionally, can be a risk factor for pulmonary metastasis of CRC. However, there has been no basic research regarding the underlying molecular mechanism. The purpose of this study was to clarify the mechanism by which smoking causes pulmonary metastasis of CRC. METHODS: First, pulmonary metastasis model mice inhaled cigarette smoke or air (control) for 1 h once a day for 3 weeks. We attempted to clarify the effect of smoking on the incidence of pulmonary metastasis. On the 15th day, CMT-93 cells were injected into the tail vein. At 6 and 8 weeks following injection, the extent of pulmonary metastasis was evaluated using in vivo micro CT. After the last CT examination, the mice were sacrificed, and the lungs were extracted for pathological examination. RESULTS: The number of mice with pulmonary metastases in the smoking group was significantly higher than in the control group. Three weeks of smoking induced mild inflammation in the lungs, as evidenced by increases in the levels of IL-6 and TNF-α in bronchoalveolar lavage. Moreover, the adhesion-related molecule ICAM-1 was overexpressed in pulmonary tissue, which allowed drained cancer cells to remain in the lung and contribute to the formation of pulmonary metastasis. CONCLUSION: Collectively, cigarette smoking may contribute to the pathogenesis and development of pulmonary metastasis in CRC through enhancement of adhesion and inflammation.

Association of surfactant protein D with pulmonary metastases from colon cancer.

Surfactant protein D (SP-D) is a member of the collectin family of proteins, which is secreted by airway epithelial cells. SP-D serves an important role in the immune system and in the inflammatory regulation of the lung. SP-D was recently found to suppress lung cancer progression by downregulating epidermal growth factor signaling. However, the relationship between SP-D and pulmonary metastases from colon cancer remains unknown. The present study aimed to determine whether SP-D may suppress the development of the mouse rectal carcinoma cell line, CMT93, in vitro. The present study investigated the effect of SP-D on pulmonary metastases from colon cancer in vivo using SP-D knockout mice. A wound healing assay and cell invasion assay revealed that SP-D suppressed the proliferation, migration and invasion of CMT-93 cells. After injection of CMT-93 cells into the tail vein, SP-D knockout mice were significantly more susceptible to developing pulmonary metastases than C57/BL6 mice (control). Moreover, a novel cell line (CMT-93 pulmonary metastasis; CMT-93 PM) was established from the lesions of pulmonary metastases in C57/BL6 mice following injection of CMT93 into the tail vein. CMT-93 PM exhibited more robust invasion and proliferation compared to CMT93, which was unaffected by exposure to SP-D. A higher incidence of pulmonary metastases was detected following injection of CMT93 PM into the tail vein of C57/BL6 mice compared with CMT-93. Consequently, SP-D may be involved in the pathogenesis of pulmonary metastases from colon cancer.

Relationship between anastomotic leakage and CT value of the mesorectum in laparoscopic anterior resection for rectal cancer.

OBJECTIVE: This study aims to indicate whether the CT value of the mesorectum could be correlated with the incidence of anastomotic leakage (AL) in laparoscopic surgery for rectal cancer. METHODS: The study subjects included 173 patients who underwent laparoscopic anterior resection (LAR) for rectal cancer from September 2005 to 2016 in our institution as well as reliable contrast-enhanced CT preoperatively. Univariate and multivariate analyses were performed to determine the correlation between surgical outcomes, including AL and CT value of the mesorectum. RESULTS: AL was observed in 30 (17.3%) patients. Amongst short-term surgical outcomes, overall complication showed significant correlation with the CT value of the mesorectum (P = 0.003). In addition, AL was the only factor, which significantly correlated with the CT value of the mesorectum (P = 0.017). By plotting receiver operating characteristic curve, -75 HU was the threshold of the CT value of the mesorectum for predicting AL with an area under the curve of 0.772. Categorized into two groups as per the threshold, low group showed significantly higher incidence of AL (OR, 2.738; 95% CI, 1.105-6.788; P = 0.030) as well as whole complications (OR, 4.431; 95%CI, 1.912-10.266; P = 0.001). CONCLUSION: The CT value of the mesorectum may be a helpful preoperative radiological biomarker to predict AL after LAR for rectal cancer.

Comparison of olanexidine versus povidone-iodine for preventing surgical site infection in gastrointestinal surgery: study protocol for a multicentre, single-blind, randomised controlled clinical trial.

INTRODUCTION: The prevalence of surgical site infection (SSI) remains higher in gastrointestinal surgery than in other surgeries. Although several guidelines have indicated the efficacy of chlorhexidine and povidone-iodine in reducing the SSI rate, the optimal recommendation has still not been established. Therefore, it is necessary to determine the more effective antiseptic for surgical site preparation. Olanexidine (1.5% olanedine, Otsuka Pharmaceutical Factory, Tokushima, Japan), which is a new antiseptic in Japan, has antimicrobial activity against a wide range of bacteria, including Gram-positive and Gram-negative bacteria. Our study will contribute to determining a new antiseptic for use in gastrointestinal and other surgeries. METHODS AND ANALYSIS: We propose a multicentre, randomised controlled clinical trial for comparing two treatments, that is, 1.5% olanexidine or 10% povidone-iodine, for surgical skin preparation to prevent SSI in clean-contaminated gastrointestinal surgeries with surgical wounds. Patients aged ≥20 years at the time of consent will be included. The primary outcome measure is the 30-day postoperative SSI rate. For the primary analysis, which is aimed at comparing the treatment effects, the adjusted risk ratio and its 95% CI will be estimated using the Mantel-Haenszel method. ETHICS AND DISSEMINATION: The protocol was first approved by the Institutional Review Board of Keio University School of Medicine, followed by the institutional review board of each participating site. Participant recruitment began in June 2018. The final results will be published in international peer-reviewed medical journals. TRIAL REGISTRATION NUMBER: UMIN 000031560; Pre-results.