Objectives: Colorectal cancer is the most prevalent malignant disease in Japan. This study aimed to publish data on colorectal cancer cases registered in 2023, involving initial treatments in 2015.

Methods: Participating facilities of the Japanese Society for Cancer of the Colon and Rectum (JSCCR) registered cases treated in 2015 according to the 8th edition of the Japanese Classification of Colorectal Carcinoma. Data sent to the National Registration Committee in 2023 were analyzed.

Results: The study analyzed 12,804 cases. Endoscopic treatments were performed in 983 cases, endoscopic treatment followed by surgical resection in 734 cases, and surgeries were carried out in 10,884 cases. Notably, the proportion of laparoscopic surgeries increased significantly from 34.7% in 2010 to 63.5% in 2015.

Conclusions: This report details the characteristics, treatment methods, and outcomes of colorectal cancer patients who received initial treatment in 2015 at JSCCR-participating facilities. These data should be helpful for patients to understand their disease accurately and for healthcare professionals to explain colorectal cancer and its treatments to patients.

Objectives: Crohn's perianal fistula represents a challenging condition to treat. Sphincters-preserving surgical techniques are increasingly being adopted as repeated surgical procedures may lead to various degrees of incontinence. This prospective study aims to assess the long-term efficacy of collagen paste application in patients with simple and complex Crohn's perianal fistulas.

Methods: Patients with Crohn's perianal fistula (simple or complex) and inactive luminal disease were enrolled. The fistula tract was treated by curettage and injection of acellular, porcine dermal collagen paste between 2019 and 2021. The primary endpoint was the clinical healing of the fistula at 12 and 24 months, defined as the absence of suppuration on clinical examination. The trial was preregistered on a public repository (ClinicalTrials.gov; NCT03776825).

Results: Fourteen patients were included in the study, ten patients (71%) had complex perianal fistula. All patients underwent previous fistula operations. Nine patients (64%) reached complete clinical remission at 12 months, two patients (14%) had a clinical recurrence six months after surgery, and three patients (21%) at 12 months follow-up. Three relapsed patients presented postoperative abscesses. Twelve patients (86%) were followed up at 24 months, no further clinical recurrences or complications were observed and the complete healing rate was 58%. No continence disturbances were recorded after collagen paste injection.

Conclusions: The results suggest that collagen paste injection may represent a safe and effective option for Crohn's perianal fistulas, worth further investigation in larger trials.

Objectives: The prognosis of patients with colorectal diverticular perforations requiring surgery is poor, and the efficacy of polymyxin B-immobilized fiber column direct hemoperfusion (PMX-DHP) in these patients has not yet been established. In the present study, we evaluated the prognostic factors and the efficacy of PMX-DHP in surgically treated patients with perforated colorectal diverticula.

Methods: Of the 116 patients with colorectal perforations who underwent emergency surgery at our hospital between April 2018 and May 2023, we retrospectively reviewed 46 patients with perforated colorectal diverticula. Preoperative, surgical, and postoperative factors were compared between the survival and mortality groups. Subgroup analysis was performed to evaluate the efficacy of PMX-DHP in severe cases.

Results: The postoperative mortality group included 7 patients (15.2%), and PMX-DHP was performed in 14 (30.4%). PMX-DHP was performed significantly more often in the mortality group (P<0.01). In multivariate analysis, antithrombotic drug administration (hazard ratio, 16.600; 95% confidence interval, 1.32-209; P<0.05) and higher lactate levels (≥ 3.0 mmol/L) (hazard ratio, 42.300; 95% confidence interval, 2.69-667, P<0.01) were independent risk factors for postoperative mortality. PMX-DHP was performed in severe cases (patients with higher lactate levels, APACHE II scores, ventilator management frequencies, and noradrenalin use). PMX-DHP was not effective in improving prognosis in severe cases.

Conclusions: Administration of antithrombotic drugs and higher lactate levels (≥ 3.0 mmol/L) are independent prognostic factors in colorectal diverticular perforations. PMX-DHP may not be effective in patients with severe preoperative conditions.

Objectives: Although some studies have evaluated the effectiveness of comprehensive genomic profiling (CGP) in solid tumors, the effectiveness of CGP in metastatic colorectal cancer (mCRC) has not been evaluated using detailed real-world long-outcome data.

Methods: This was part of a single institutional non-comparative prospective observational study that observed all patients with solid tumors who underwent CGP at Saitama Medical Center, Saitama Medical University. We enrolled patients with mCRC between June 4, 2020, and March 31, 2023. The primary endpoint was the proportion of patients who received CGP-based therapy.

Results: There were 43 patients with mCRC. Of these, six patients (14.0%) received CGP-based therapy. The median overall survival from CGP testing in patients who received CGP-based therapy was 9.7 months. The progression free survival (PFS) ratio of CGP-based therapy and immediate previous therapy ranged from 0.04 to 2.0. The PFS ratio >1.5 was 14.3% (one out of seven treatments). One patient exhibited an exceptional response to pembrolizumab. Before CGP testing, the patient's cancer was classified as non-microsatellite instability-high, although the CGP test revealed a high tumor mutational burden. In Japan, patients with this subtype cannot undergo pembrolizumab without testing for CGP.

Conclusions: This prospective observational study's findings provide an overview of CGP testing outcomes in patients with refractory mCRC.

Objectives: The present study examined the incidence of incisional hernia by comparing patients from whom a specimen was extracted either through a Pfannenstiel incision (PI) with an intracorporeal anastomosis or via a midline incision (MI) with an extracorporeal anastomosis.

Methods: The records of 370 consecutive patients who underwent a laparoscopic or robotically-assisted colectomy were retrospectively analyzed. Regardless of the clinical symptoms, incisional hernia was objectively diagnosed based on abdominal computed tomography findings. The surgical outcomes and incisional hernia incidence were retrospectively compared between the groups. Propensity score matching (PSM) was used to balance background differences between the groups.

Results: Eighty-seven and 283 patients were in the PI group and MI group, respectively. After PSM, 71 patients were selected from each group. The median observation time was 572 and 1110 days in the PI and MI group, respectively. The PI group had no incidence of incisional hernia whereas the MI group had a 14% incidence, demonstrating that the former had significantly fewer incisional hernias (p=0.0014). The median interval from surgery to incisional hernia development was 295 days. The PI with an intracorporeal anastomosis was not associated with an increased complication rate.

Conclusions: The PI was preferable for intraoperative specimen extraction owing to the low, associated incidence of incisional hernia.

Objectives: This study was performed to investigate the efficacy of nonoperative treatment of uncomplicated sigmoid volvulus (SV) using a transanal decompression tube (TDT).

Methods: This was a single-center retrospective study in patients with SV treated between 2008 and 2021. For uncomplicated patients, nonoperative decompression of any of four types was performed: decompression with a colonoscope (CS), TDT without CS, TDT with CS (tip in the sigmoid colon), and TDT with CS (tip in the descending colon).

Results: A total of 72 patients with 109 admissions were enrolled in the study. Of these, 69 patients with uncomplicated SV were initially managed nonoperatively, whereas no procedures were performed in three patients due to presentation with septic shock on arrival. Of the 69 patients, 11 underwent surgery and two refused surgical management. Three patients showed improved CS without TDT. Among 53 patients who improved nonoperatively with TDT, 14 (26.4%) experienced recurrence with a median (range) time to recurrence of 603 (43-2714) days. No early recurrence was observed. Of a total of 106 cases with decompression, 97 (91.5%) were performed with TDT and all were completed without complications. The median (range) duration of decompression using TDT in these 81 cases without surgery was 5 (2-11) days. In the Cox proportional hazards regression model, only previous history of SV was associated with recurrence (hazard ratio 3.60; 95% confidence interval 1.24-10.46, p = 0.02).

Conclusions: Decompression using TDT is safe, effective, and may reduce the rate of recurrence in patients with uncomplicated SV.

Objectives: In advanced left-sided colorectal cancer, cutting the root of the inferior mesenteric artery (IMA) branching from the aorta is recommended for complete lymph node dissection. However, this procedure sometimes causes severe complications. This study aimed to elucidate the lymph nodes' distribution around the IMA and identify the most critical sites for lymph node dissection.

Methods: This study included 30 consecutive patients with left-sided colorectal cancer who underwent curative resection with main lymph node dissection in a single institution between January and June of 2022. The mesenteric sections (main lymph nodes, IMA, left colic artery [LCA], and inferior mesenteric vein) were removed from the surgically excised specimen. Subsequently, whole-tissue sections were prepared and stained with hematoxylin and eosin. The positional relationships between each blood vessel and respective lymph nodes were then assessed using the pathological findings.

Results: The main lymph nodes were identified in 26 out of 30 patients. The total number of dissected lymph nodes per patient was 0-30 (average: 5.3), and the median distance from the IMA to the main lymph node was 7.61 mm (1.87-43.26 mm). Dividing the lymph nodes into segments, we found 18%, 46%, and 36% of the lymph nodes in the proximal, middle, and distal segments, respectively. Additionally, all lymph nodes were found outside of the IMA sheath surrounding each arterial wall.

Conclusions: In left-sided colorectal cancer, the main lymph nodes are mostly located around the LCA bifurcation, which may be essential to ensure main lymph node dissection for advanced stage cases.

Objectives: To explore the predictive performance on the need for surgical intervention in patients with adhesive small bowel obstruction (ASBO) using machine-learning (ML) algorithms and investigate the optimal timing for transition to surgery.

Methods: One hundred and six patients with ASBO who initially underwent long transnasal intestinal tube (LT) decompression were enrolled in this retrospective study. Traditional logistic regression analysis and ML algorithms were used to evaluate the risk of need for surgical intervention.

Results: Non-operative management (NOM) by LT decompression failed in 28 patients (26%). Multivariate logistic regression analysis identified a drainage volume ≥665 ml via LT on day 1, interval between ASBO diagnosis and LT intubation, and small bowel dilatation at 48 h after LT intubation to be independent predictors of transition to surgery (odds ratios 7.10, 1.42, and 19.81, respectively; 95% confidence intervals 1.63-30.94, 1.00-2.02, and 3.04-129.10; P-values 0.009, 0.047, and 0.002). The random forest algorithm showed the best predictive performance of five ML algorithms tested, with an area under the curve of 0.889, accuracy of 0.864, and precision of 0.667 in the test set. 97.4% of patients without transition to surgery (n=78) had passes of first flatus until three days.

Conclusions: This is the first study to demonstrate that ML algorithm can predict the need for surgery in patients with ASBO. The guideline recommended period for initial NOM of 72 h seems to be reasonable. These findings can be used to develop a framework for earlier clinical decision-making in these patients.

Objectives: To date, there have been no reports on the long-term effects of a method that combines external hemorrhoidectomy with aluminum potassium sulfate and tannic acid (ALTA) sclerotherapy. This study aimed to investigate the efficacy and safety of external hemorrhoidectomy combined with ALTA sclerotherapy (EA) in reducing postoperative complications associated with conventional hemorrhoidectomy.

Methods: EA was performed under sacral epidural anesthesia, and ALTA sclerotherapy was applied to the remaining internal hemorrhoids after resection of the external hemorrhoids. Mixed internal and external hemorrhoids were treated with EA, whereas internal hemorrhoids without external hemorrhoids were treated with ALTA sclerotherapy. The three EA patterns were defined as EA1, EA2, and EA3, depending on the number of EAs performed.

Results: This study included 3,403 patients who underwent EA for grade II-IV mixed hemorrhoids. EA1 was the most common, with 1,789 (52.6%) cases, followed by EA2 (36.2%) and EA3 (11.2%). Postoperative complications occurred in 120 (3.5%) patients and increased with the number of EAs, with fever and bleeding being common in the early postoperative period, and perianal abscess and/or fistula being common after 1 month. The mean postoperative follow-up period was 26.4 months, and 136 (4.0%) patients underwent reoperation for recurrent internal or mixed hemorrhoids. The reoperation rate for EA1 was significantly higher than that for EA2 and EA3. The 5- and 10-year cumulative recurrence-free rates were 92.5% and 67.2%, respectively.

Conclusions: EA is as curative as conventional hemorrhoidectomy and reduces postoperative complications. Therefore, EA is the preferred procedure for patients with mixed hemorrhoids.

Objectives: The aim of the study was to investigate the differences in clinical characteristics and surgical outcomes between para-colostomy hernia (PCH) and para-ileal-conduit hernia (PICH) after laparoscopic repairs.

Methods: We retrospectively analyzed data from 41 laparoscopic parastomal hernia repairs performed at the Jikei University Daisan Hospital between June 2012 and September 2023. The data were divided into PCH (n=31) and PICH (n=10) groups and compared.

Results: The comparison of patient backgrounds and hernia characteristics showed no significant differences between PCH and PICH groups. Surgical procedures included laparoscopic Sugarbaker repair (LSB) for PCH (29 cases) and PICH (8 cases), and endoscopic Pauli repair (ePauli) for both PCH (2 cases) and PICH (2 cases). Intraoperative findings indicated a significantly higher rate of severe intra-abdominal adhesions (Zühlke index III/IV) in the PICH group (60%) compared to the PCH group (23%) (p=0.0485). The median operation time was significantly longer for PICH (223 [120-423] minutes) than for PCH (158 [48-386] minutes) (p=0.0467). Perioperative complications occurred in 1 PCH case (3%) and 2 PICH cases (20%), with no significant difference in postoperative hospital stay (9 [4-19] vs. 9 [6-14] days). With the follow-up period of 57 [2-110] months for PCH and 52 [20-104] months for PICH, recurrence was observed in 4 PCH cases (12%) but not statistically significant.

Conclusions: The comparison of PCH and PICH suggests that PICH is associated with more severe intra-abdominal adhesions and longer operation times, indicating higher operative difficulty. Therefore, it would be advisable to discuss the surgical outcomes of repair for these stomas separately.

Objectives: Serrated polyposis syndrome (SPS) is a rare condition associated with an increased risk of colorectal cancer. However, the genetic basis of SPS in Japanese patients remains unclear. The present study therefore aimed to address this omission by identifying candidate causative genes of SPS in Japanese patients.

Methods: The present study performed next-generation sequencing using a multigene panel to identify the causative genes in SPS. Whenever a candidate gene was detected, whole exome sequencing of the tumor tissue was performed.

Results: An analysis of 11 patients with SPS identified a germline pathogenic variant of BUB1 (c.1543G>T/p.Gly515Ter) in a 47-year-old, female patient with transverse colon cancer with more than 50 serrated polyps. She had no history of smoking. None of the canonical, causative genes in common colorectal cancer, such as APC, KRAS and TP53, were detected in her lesion. Most of the somatic variants detected in the cancer were transition substitutions (C>T).

Conclusions: BUB1 was identified as a candidate causative gene in SPS in a non-smoker with the disease. These findings will hopefully contribute to understanding the genetic basis of SPS.

Objectives: To investigate the significance of lateral pelvic lymph node dissection (LPLND) in resectable stage IV low rectal cancers, reviewing the treatment outcomes from a single cancer center dedicated to LPLND.

Methods: Consecutive 56 patients with stage IV low rectal cancers who underwent primary tumor resection (PTR) between 2007 and 2022 were identified. Sixteen patients with non-curative PTR were excluded, and 40 with curative PTR were analyzed.

Results: The dominant metastatic organ was the liver in 30 (75.0%) patients, followed by the lung in 9 (22.5%). Seven (17.5%) patients had multiple organ metastasis. Five of 40 patients had cT1bN0 or cT2N0 disease, 8 did not receive LPLND for other reasons, and accordingly, 27 (67.5%) finally received LPLND. A total of 15 patients (37.5% of all 40 cases and 55.5% of 27 LPLND cases) had LPLN metastasis. Six (15.0%) patients had bilateral metastasis, and 6 (15.0%) had LD3 metastasis. Eight (20.0%) patients developed local recurrence (LR), and the 5Y-LR rate was 22.3%. Twelve (30.0%) patients underwent preceding chemotherapy before PTR, 26 (65.0%) received chemotherapy after PTR, and 23 (57.5%) achieved complete resection. Twelve (52.2%) of 23 patients developed distant recurrence after complete resection. 5Y-overall survival for all patients was 42.4%.

Conclusions: A high rate of LPLN metastasis implies the significance of management for LPLN metastasis; meanwhile, an unsatisfactory complete resection rate and overall survival implies that LPLN metastasis in this cohort should be dealt with as a systemic disease.

Objectives: Peritoneal metastasis indicates a poor prognosis in patients with colorectal cancer (CRC). Studies have shown improved prognosis in patients after removal of peritoneal dissemination, and this surgery is recommended if not excessively invasive. The aim of this study was to examine clinical outcomes and prognostic factors for R0 resected CRC with synchronous peritoneal metastasis.

Methods: We analyzed data retrospectively from 250 patients with stage IV CRC who underwent R0 resection at our hospital. The patients were divided into three groups according to the type of surgery: non-resected (N), palliative primary tumor resection (P), and R0 resection (R0) groups. Overall survival (OS) and recurrence-free survival (RFS) were investigated and clinicopathological parameters were analyzed for prognostic significance.

Results: The 3-year OS was 57.2% in the R0 group. The R0 group had a significantly higher 3-year OS than that in the other groups (p < 0.0001). Multivariate analysis revealed that histological type, lymphatic and venous invasion, liver metastasis, R0 resection, and perioperative chemotherapy were independent prognostic factors. The 5-year RFS in the R0 group was 26.5%. Multivariate analysis revealed that the number of peritoneal metastases and surgical procedure were independent prognostic factors. Laparoscopic surgery had better 5-year RFS in the R0 group compared with that in the open surgery group (p = 0.0044).

Conclusions: R0 resection of colorectal cancer with synchronous peritoneal metastasis should be considered for improving long-term survival. The laparoscopic approach for this disease is another promising method to prolong survival in patients with R0 resection.

Objectives: This study aimed to investigate preoperative factors, including the C-reactive protein (CRP) /albumin ratio (CAR), associated with postoperative outcomes in patients with colorectal perforation who underwent emergency surgery to improve postoperative prognosis.

Methods: Twenty-eight consecutive patients who underwent emergency surgery for colorectal perforations were included. We retrospectively investigated the clinical factors associated with their postoperative outcomes.

Results: The median patient age was 69.5 years (range, 46.0-93.0 years); 13 patients (46.4%) were males and 15 (53.6%) were females. Colorectal cancer (8 [28.6%]) was the most common cause of colorectal perforation. Postoperative complications were diagnosed in 18 patients (64.3%), with intraabdominal abscess as the most common (6 [21.4%]). Multivariate analysis revealed that CAR (odds ratio, 1.357; 95% confidence interval, 1.056-1.743; p=0.017) was an independent risk factor for postoperative complications. A cutoff value of 4.9 was selected to predict the development of postoperative complications based on the CAR. The proportion of all postoperative complications (p=0.016), postoperative complications of Clavien-Dindo classification grade II or higher (p=0.002), and death during hospitalization (p=0.049) were significantly higher in the group of patients with CAR ≥ 4.9 than in those with CAR < 4.9. Additionally, intraabdominal abscess (p=0.049) was significantly higher in the group of patients with a non-improvement in CAR on postoperative day 3 than in those with an improvement in CAR on postoperative day 3.

Conclusions: Perioperative CAR could be a predictor of perioperative complications and death and might be useful in improving the postoperative prognosis of colorectal perforations.

Objectives: The prognostic significance of a high visceral fat area (VFA) in metastatic colorectal cancer (mCRC) remains unclear. We evaluated the prognostic impact of high-VFA on the long-term outcomes of patients with mCRC who underwent chemotherapy.

Methods: Ninety patients with metastatic CRC who underwent chemotherapy were included. VFA measurement was performed by pre-treatment computed tomography using image analysis system. Overall survival (OS) and progression-free survival (PFS) rates were analyzed using the Cox proportional hazards model and Kaplan-Meier curves with the log-rank test.

Results: High-VFA was identified in 39 patients. The OS (2-year OS rates: 51.6% vs 33.3%, p=0.0023) and PFS rates (2-year PFS rates: 18.0% vs 2.7%, p=0.012) were significantly lower in the high-VFA group than in the low-VFA group. In multivariate analysis, the independent significant predictors of OS were carbohydrate antigen 19-9 (CA19-9) ≥37.0 U/mL (HR: 1.99, 95%CI [1.20-3.31], p=0.007), Glasgow prognostic score (GPS) of 1 or 2 (HR: 2.65, 95%CI [1.53-4.58], p<0.001), and high-VFA (HR: 3.09, 95%CI [1.81-5.25], p<0.001). Similarly, the independent significant predictors of PFS were CA19-9 ≥37.0 U/mL (HR: 2.02, 95%CI [1.21-3.38], p=0.007), GPS of 1 or 2 (HR: 1.87, 95%CI [1.17-2.99], p=0.008), and high-VFA (HR: 2.65, 95% CI [1.61-4.35], p<0.001).

Conclusions: We demonstrated that pre-treatment high-VFA and high-GPS were significantly associated with worse OS and PFS rates in patients with mCRC who underwent chemotherapy.

Objectives: Some patients with lower rectal cancer develop "skip metastasis," in which lymph node metastasis occurs in the lateral but not the mesenteric lymph nodes. However, the prognostic impact of skip metastasis is unclear. This study aimed to determine the long-term prognosis of skip metastasis in lower rectal cancer.

Methods: This retrospective study included patients with stage I-III lower rectal cancer who underwent total mesorectal excision and lateral lymph node dissection at our institution between 2000 and 2019. We investigated the association of lymph node metastasis with relapse-free and overall survival. Multivariate analyses were performed using Cox proportional hazards regression models.

Results: Of a total of 371 patients, 183 (49%) were negative for lymph node metastasis, 115 (31%) were positive for mesenteric lymph nodes only, 18 (5%) were positive for lateral lymph nodes only (skip metastasis), and 55 (15%) were positive for both mesenteric and lateral lymph nodes; the 5-year relapse-free survival rates were respectively 79.9%, 60.0%, 68.3%, and 32.7%, and 5-year overall survival rates were 96.6%, 90.0%, 85.6%, and 57.3%. Multivariable analysis revealed significant differences in relapse-free and overall survival between those positive for both mesenteric and lateral lymph nodes and those positive for lateral lymph nodes only (relapse-free survival, hazard ratio 2.30, p=0.048; overall survival, hazard ratio 3.50, p=0.030).

Conclusions: In patients with lower rectal cancer who underwent total mesorectal excision and lateral lymph node dissection, those with skip metastasis had better relapse-free and overall survival than those with both mesenteric and lateral lymph node metastases.

Objectives: This study evaluated the endoscopic management and clinical outcomes of patients with colonic diverticular bleeding (CDB) during the coronavirus disease 2019 (COVID-19) pandemic.

Methods: A total of 388 hospitalized patients diagnosed with CDB at two hospitals during (April 2020-March 2023) and before (April 2017-March 2020) the pandemic were enrolled in the study. We performed one-to-one propensity score matching (PSM) on the participants. We analyzed endoscopic management and clinical outcomes before and during the pandemic using a total of 264 patients matched in a PSM analysis.

Results: A total of 213 (1.3%) and 172 (1.2%) colonoscopies were performed before and during the pandemic, respectively in patients with CDB (P = 0.70). After PSM, the number of early colonoscopies (63.6% vs. 76.5%, P = 0.03) and colonoscopies performed outside regular working hours (23.8% vs. 47.7%, P < 0.01) was significantly lower during the pandemic than before it. A univariate logistic regression analysis revealed that the risks of rebleeding within 30 days (odds ratio [OR]: 0.81, P = 0.42) and composite outcome (OR: 0.90, P = 0.69) were not increased during the pandemic.

Conclusions: During the pandemic, the number of early colonoscopies and colonoscopies performed outside regular working hours decreased; however, this decrease did not influence rebleeding and composite outcome in patients with CDB.

In Japan, pharmaceutical approval for the use of the da Vinci SP (dV SP) Surgical System in colorectal cancer surgery was obtained in September 2022. This system has an operating arm with three instruments and one scope to be manipulated through a single incision in colorectal cancer surgery. An 88-year-old female presented to our hospital with melena and was diagnosed with cStage IIa descending colon cancer (cT3N0M0). The patient underwent left hemicolectomy with the dV SP using an Access Port kit. The Access Port kit was inserted into a 3-cm vertical skin incision at the umbilicus. With only this surgical wound, mobilization from the rectum to the colon, and lymph node dissection were performed. Herein, we report the world's first descending colon cancer resection with the dV SP using an Access Port kit.

This report and literature review explores cases of tumor cell implantation at colorectal post-endoscopic resection sites. We detail a unique case in which advanced rectosigmoid colon cancer cells would implant into an endoscopic submucosal dissection (ESD) site in a synchronous upper rectal colon intramucosal cancer. The patient underwent upper rectal ESD prior to surgery for the advanced rectosigmoid colon cancer. After 7 months, a follow-up colonoscopy revealed recurrence at the upper rectal ESD scar, and the patient underwent Miles' operation. The recurrence was confirmed by RAS mutation status to be implantation from the advanced rectosigmoid colon cancer.

The literature review, encompassing ten cases, shows that implantation often occurs at rectal post-endoscopic resection sites, with some cases associated with nearby advanced cancers, particularly on the oral side. Four cases suggested implantation from cancer during ESD. These findings underscore the need for caution during colorectal ESD procedures, considering the potential implantation risk. Additionally, early detection of implantation and subsequent curative resection were common outcomes, suggesting the importance of vigilant surveillance. Further research and preventive measures such as thorough intraluminal lavage and complete closure of ulcers may be crucial in minimizing implantation risks post-endoscopic treatment.

Although colorectal cancer frequently invades adjacent organs, colon-to-colon invasion is rarely observed, and colo-colonic fistula formation due to colorectal cancer is uncommon. Here we report a case of preoperative diagnosis of cecal cancer that has invaded the transverse colon. A 69-year-old woman presented with diarrhea and a palpable mass in the lower right abdomen. After being diagnosed with double cancer involving the cecum and transverse colon at a previous hospital, she was referred to our hospital. CT scans revealed enhanced mass-like wall thickening in both the cecum and transverse colon, with 3D-CT suggesting a cecal tumor invading the transverse colon. The accurate preoperative diagnosis and prediction of fistula formation led us to perform curative en bloc resection using laparoscopic surgery. The resected specimen contained an ulcerated moderately differentiated adenocarcinoma measuring 6.0 cm× 4.5 cm in the cecum. Additionally, a fistula originating from the cecal cancer and communicating with the transverse colon was identified. The tumor was classified as stage IIIC (T4b, N1, M0). When multiple masses are identified in the colon, it is important to consider the possibility of the primary tumor invading neighboring organs and the potential for fistula formation.