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Resistance to neoadjuvant chemoradiation therapy (neo-CRT) is a significant clinical problem in the treatment of locally advanced rectal cancer. Identification of novel therapeutic targets and biomarkers predicting therapeutic response is required to improve patient outcomes. Increasing evidence supports a role for the complement system in resistance to anti-cancer therapy. In this study, increased expression of complement effectors C3 and C5 and increased production of anaphylatoxins, C3a and C5a, was observed in radioresistant rectal cancer cells. Modulation of the central complement effector, C3, was demonstrated to functionally alter the radioresponse, with C3 overexpression significantly enhancing radioresistance, whilst C3 inhibition significantly increased sensitivity to a clinically-relevant dose of radiation. Inhibition of C3 was demonstrated to increase DNA damage and alter cell cycle distribution, mediating a shift towards a radiosensitive cell cycle phenotype suggesting a role for C3 in reprogramming of the tumoural radioresponse. Expression of the complement effectors C3 and C5 was significantly increased in human rectal tumour tissue, as was expression of CFB, a component of the alternative pathway of activation. Elevated levels of C3a and C5b-9 in pre-treatment sera from rectal cancer patients was associated with subsequent poor responses to neo-CRT and poorer survival. Together these data demonstrate a role for complement in the radioresistance of rectal cancer and identify key complement components as potential biomarkers predicting response to neo-CRT and outcome in rectal cancer.

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INTRODUCTION: Goblet cell carcinoid (GCC) is a rare and poorly understood appendiceal neoplasm, exhibiting mixed histological and aggressive clinical features. Current guidelines recommend right hemicolectomy in all cases, although there is conflicting evidence that appendicectomy alone may be sufficient. This review aims to identify the optimal surgical management for appendiceal GCC. METHODS: A systematic review was performed by searching MEDLINE, Embase, Scopus and the Cochrane Register of Controlled Trials. Randomised controlled trials, cohort studies or large case series (>5 patients) reporting clinical outcomes for patients undergoing surgical management of GCC of the appendix were included. Outcomes extracted included participant and tumour characteristics, type of surgery and survival data. RESULTS: A total of 1341 studies were retrieved. After duplicate removal, 796 titles were screened for relevance prior to abstract and full text review. A total of six studies were included for analysis, comprising 3177 patients-1629 females and 1548 males. The median age ranged from 51 to 72 years. A total of 2329 patients underwent right hemicolectomy, while 824 were treated with appendicectomy only. Overall, the included studies report increased survival in patients undergoing right hemicolectomy compared to appendicectomy alone. A meta-analysis was not possible due to insufficient data reported in the published literature to date. CONCLUSIONS: There is no consensus regarding the optimal surgical management of appendiceal GCC, as outcomes-based data comparing surgical interventions are lacking. It is possible that some patients with favourable features are overtreated. The absence of robust evidence to support a more conservative approach means that right hemicolectomy remains the standard of care for all patients, in keeping with current international guidelines. The rarity of this condition and limited data in the published studies remain barriers to evidence-based best clinical practice.

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This systematic review investigates the potential of circulating tumour DNA (ctDNA) as a predictive biomarker in the management and prognosis of squamous cell carcinoma of the anal canal (SCCA). PubMed, EMBASE, and Cochrane Central Registry of Controlled Trials were searched until 7 January 2024. Selection criteria included research articles exploring ctDNA in the context of anal cancer treatment response, recurrence risk assessment, and consideration of salvage surgery. A total of eight studies were therefore included in the final review, examining a total of 628 patients. These studies focused on three main themes: SCCA diagnosis and staging, treatment response, and patient outcomes. Significant heterogeneity was observed in terms of patient cohort, study methodology, and ctDNA biomarkers. Four studies provided information on the sensitivity of ctDNA biomarkers in SCCA, with a range of 82-100%. Seven studies noted a correlation between pre-treatment ctDNA levels and SCCA disease burden, suggesting that ctDNA could play a role as a biomarker for the staging of SCCA. Across all seven studies with paired pre- and post-treatment ctDNA samples, a trend was seen towards decreasing ctDNA levels post-treatment, with specific identification of a 'fast elimination' group who achieve undetectable ctDNA levels prior to the end of treatment and may be less likely to experience treatment failure. Residual ctDNA detection post-treatment was associated with poorer patient prognosis. This systematic review identifies the broad potential of ctDNA as a useful and decisive tool in the management of SCCA. Further analysis of ctDNA biomarkers that include larger patient cohorts is required in order to clearly evaluate their potential role in clinical decision-making processes.

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PURPOSE/AIM: Perianal wound healing and/or complications are common following abdominoperineal resection (APR). Although primary closure is commonly undertaken, myocutaneous flap closure such as vertical rectus abdominis myocutaneous flap (VRAM) is thought to improve wound healing process and outcome. A comprehensive meta-analysis was performed to compare outcomes of primary closure versus VRAM flap closure of perineal wound following APR. METHODS: PubMed, MEDLINE, EMBASE, and Cochrane Central Registry of Controlled Trials were comprehensively searched until the 8th of August 2023. Included studies underwent meta-analysis to compare outcomes of primary closure versus VRAM flap closure of perineal wound following APR. The primary outcome of interest was perineal wound complications, and the secondary outcomes were abdominal wound complications, dehiscence, wound healing time, length of hospital stay, and mortality. RESULTS: Ten studies with 1141 patients were included. Overall, 853 patients underwent primary closure (74.8%) and 288 patients underwent VRAM (25.2%). Eight studies reported on perineal wound complications after APR: 38.2% (n = 263/688) in the primary closure group versus 32.8% (n = 80/244) in the VRAM group. Perineal complication rates were statistically significantly lower in the VRAM group versus primary closure ((M-H OR, 1.61; 95% CI 1.04-2.49;

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INTRODUCTION: The management of anal cancer relies on clinical and histopathological features for treatment decisions. In recent years, the field of radiomics, which involves the extraction and analysis of quantitative imaging features, has shown promise in improving management of pelvic cancers. The aim of this study was to evaluate the current application of radiomics in the management of anal cancer. METHODS: A systematic search was conducted in Medline, EMBASE, and Web of Science databases. Inclusion criteria encompassed randomized and non-randomized trials investigating the use of radiomics to predict post-operative recurrence in anal cancer. Study quality was assessed using the QUADAS-2 and Radiomics Quality Score tools. RESULTS: The systematic review identified a total of nine studies, with 589 patients examined. There were three main outcomes assessed in included studies: recurrence (6 studies), progression-free survival (2 studies), and prediction of human papillomavirus (HPV) status (1 study). Radiomics-based risk stratification models were found to provide valuable insights into treatment response and patient outcomes, with all developed signatures demonstrating at least modest accuracy (range: .68-1.0) in predicting their primary outcome. CONCLUSION: Radiomics has emerged as a promising tool in the management of anal cancer. It offers the potential for improved risk stratification, treatment planning, and response assessment, thereby guiding personalized therapeutic approaches.

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Radiogenomics, a sub-domain of radiomics, refers to the prediction of underlying tumour biology using non-invasive imaging markers. This novel technology intends to reduce the high costs, workload and invasiveness associated with traditional genetic testing via the development of 'imaging biomarkers' that have the potential to serve as an alternative 'liquid-biopsy' in the determination of tumour biological characteristics. Radiogenomics also harnesses the potential to unlock aspects of tumour biology which are not possible to assess by conventional biopsy-based methods, such as full tumour burden, intra-/inter-lesion heterogeneity and the possibility of providing the information of tumour biology longitudinally. Several studies have shown the feasibility of developing a radiogenomic-based signature to predict treatment outcomes and tumour characteristics; however, many lack prospective, external validation. We performed a systematic review of the current literature surrounding the use of radiogenomics in rectal cancer to predict underlying tumour biology.

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BACKGROUND: Mean corpuscular volume (MCV) has been shown to have some correlation to oncological outcomes in oesophageal cancer, with high pre-operative MCV associated with disease recurrence. A similar association has previously been reported in colorectal cancer. AIMS: This study is aimed at investigating whether high MCV bears similar relation to post-operative outcome and disease recurrence in colorectal cancer (CRC). METHODS: Patients undergoing elective CRC resection with curative intent between January 2008 and December 2019 were identified from our prospective database. Review of patient demographic details, American Society of Anaesthesiologists (ASA) grade, smoking and alcohol intake were performed. In addition, tumour location and staging, operation performed, pre-operative laboratory data and oncological management of each patient were noted. Post-operative morbidity (Clavien-Dindo (CD) score > 2), 30-day mortality, in-hospital mortality and cancer recurrence were examined and multivariable regression analysis was performed to predict these outcomes. RESULTS: A total of 1,293 CRCs were resected, with 1,159 patients (89.7%) experiencing a hospital course without major morbidity (CD < 3). 30-day mortality rate was less than 1% (12/1293). There were 176 patients (13.6%) with recurrence at follow-up. When multivariable regression analysis was performed, high pre-operative MCV did not predict negative post-operative or oncological outcomes. CONCLUSION: MCV does not appear to be an independent prognostic factor for outcomes following elective CRC resection.

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INTRODUCTION: Historically, surgical resection for patients with locally recurrent rectal cancer (LRRC) had been reserved for those without metastatic disease. 'Selective' patients with limited oligometastatic disease (OMD) (involving the liver and/or lung) are now increasingly being considered for resection, with favourable five-year survival rates. METHODS: A retrospective analysis of consecutive patients undergoing multi-visceral pelvic resection of LRRC with their oligometastatic disease between 1 January 2015 and 31 August 2021 across four centres worldwide was performed. The data collected included disease characteristics, neoadjuvant therapy details, perioperative and oncological outcomes. RESULTS: Fourteen participants with a mean age of 59 years were included. There was a female preponderance (n = 9). Nine patients had liver metastases, four had lung metastases and one had both lung and liver disease. The mean number of metastatic tumours was 1.5 +/- 0.85. R0 margins were obtained in 71.4% (n = 10) and 100% (n = 14) of pelvic exenteration and oligometastatic disease surgeries, respectively. Mean lymph node yield was 11.6 +/- 6.9 nodes, with positive nodes being found in 28.6% (n = 4) of cases. A single major morbidity was reported, with no perioperative deaths. At follow-up, the median disease-free survival and overall survival were 12.3 months (IQR 4.5-17.5 months) and 25.9 months (IQR 6.2-39.7 months), respectively. CONCLUSIONS: Performing radical multi-visceral surgery for LRRC and distant oligometastatic disease appears to be feasible in appropriately selected patients that underwent good perioperative counselling.

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Resistance to neoadjuvant chemoradiation therapy, is a major challenge in the management of rectal cancer. Increasing evidence supports a role for altered energy metabolism in the resistance of tumours to anti-cancer therapy, suggesting that targeting tumour metabolism may have potential as a novel therapeutic strategy to boost treatment response. In this study, the impact of metformin on the radiosensitivity of colorectal cancer cells, and the potential mechanisms of action of metformin-mediated radiosensitisation were investigated. Metformin treatment was demonstrated to significantly radiosensitise both radiosensitive and radioresistant colorectal cancer cells in vitro. Transcriptomic and functional analysis demonstrated metformin-mediated alterations to energy metabolism, mitochondrial function, cell cycle distribution and progression, cell death and antioxidant levels in colorectal cancer cells. Using ex vivo models, metformin treatment significantly inhibited oxidative phosphorylation and glycolysis in treatment naïve rectal cancer biopsies, without affecting the real-time metabolic profile of non-cancer rectal tissue. Importantly, metformin treatment differentially altered the protein secretome of rectal cancer tissue when compared to non-cancer rectal tissue. Together these data highlight the potential utility of metformin as an anti-metabolic radiosensitiser in rectal cancer.

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BACKGROUND: Synchronous para-aortic lymph node metastasis (PALNM) in colorectal cancer (CRC) is a relatively rare clinical entity. There is a lack of consensus on management of these patients, and the role of para-aortic lymph node dissection (PALND) remains controversial. This systematic review aims to describe the survival outcomes in colorectal cancer with synchronous PALNM when lymph node dissection is performed. METHODS: A systematic review of Pubmed, Embase and Web of Science databases for PALND in CRC was performed. Studies including patients with synchronous PALNM undergoing resection with curative intent, published from the year 2000 onwards, were included. RESULTS: Twelve retrospective studies were included. Four studies reported survival outcomes for rectal cancer, two for colon cancer and six as colorectal. Survival outcomes for 356 patients were included. Average 5-year overall survival (OS) was 22.4%, 33.9% and 37.7% in the rectal, colon and colorectal groups respectively. Three year OS in the groups was 53.6%, 46.2% and 65.7%. CONCLUSION: There remains a lack of quality data to confidently make recommendations regarding the management of synchronous PALNM in colon and rectal cancer cohorts. Retrospective data suggests a benefit in highly selective cohorts and therefore a case-by-case evaluation remains the standard of care.

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BACKGROUND: Primary mucosal anorectal malignant melanoma (AMM) is an invasive malignancy with poor survival. Management options have been variable, due to limited data and lack of randomised control trials available on the optimal surgical strategy. The aim of this review was to compare local excision versus radical resection. METHODS: A systematic search of articles in PubMed, Ovid, Scopus, and the Cochrane Library database was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The outcomes of interest were the impact that surgical strategy had on survival (primary) and recurrence rates (secondary) for the treatment of AMM, comparing sphincter sparing local excision (LE) versus extensive abdominoperineal resection (APR). RESULTS: Ten studies met the predefined criteria. Overall, there were 303 patients, with a median age of 58.2 years. Sixty-one percent (n = 187/303) had radical surgery (abdominoperineal resection) for the primary treatment of AMM. Overall, 5-year survival for the APR and LE was 23% and 32% respectively. Meta-analysis on the median OS noted no statistical difference between the two groups. However, local recurrence occurred in 20.82% and 47.04% in the APR and LE groups respectively. Meta-analysis observed a statistically significant reduction in recurrence when patients had an APR as primary treatment (OR 0.15, 95% CI = 0.08-0.28, p < 0.00001). CONCLUSION: Though local recurrence rates are more common with local excision of AMM, this does not confer an inferior OS when comparing LE versus APR. The decision to proceed with LE vs. APR should be made on a case-by-case basis.

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AIM: There is a current lack of evidence in the literature to support the routine use of negative pressure wound therapy (NPWT) to reduce the risk of surgical site infections (SSI) in the setting of ileostomy or colostomy reversal. The aim of this study is to examine whether routine NPWT confers a lower rate of SSI than conventional dressings following reversal of ileostomy or colostomy. METHODS: The PRIC study is a randomized, controlled, open-label, multi-centre superiority trial to assess whether routine NPWT following wound closure confers a lower rate of SSI following reversal of ileostomy or colostomy when compared to conventional dressings. Participants will be consecutively identified and recruited. Eligible participants will be randomized in a 1:1 allocation ratio, to receive either the NPWT (PREVENA) dressings or conventional dressings which will be applied immediately upon completion of surgery. PREVENA dressings will remain applied for a duration of 7 days. Surgical wounds will then be examined on post-operative day seven as well as during follow-up appointments in OPD for any evidence of SSI. In the interim, public health nurses (PHN) will provide out-patient support services incorporating wound assessment and care as part of a routine basis. Study investigators will liaise with PHN to gather the relevant data in relation to the time to wound healing. Our primary endpoint is the incidence of SSI within 30 days of stoma reversal. Secondary endpoints include measuring time to wound healing, evaluating wound healing and aesthetics and assessing patient satisfaction. CONCLUSION: The PRIC study will assess whether routine NPWT following wound closure is superior to conventional dressings in the reduction of SSI following reversal of ileostomy or colostomy and ascertain whether routine NPWT should be considered the new standard of care.

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INTRODUCTION: Colorectal cancer (CRC) outcomes vary depending on tumour biology, with several features used to predict disease behaviour. Extramural venous invasion (EMVI) is associated with negative outcomes and its presence has been established as an indicator of more aggressive disease in CRC. METHODS: A prospectively maintained database was examined for patients undergoing curative resection for non-metastatic CRC between 2012 and 2018 in a tertiary institution. Clinicopathological factors were compared to assess their impact on recurrence, all-cause mortality and cancer-related death. Kaplan Meier analysis of the association between EMVI and these endpoints was performed, and univariable and multivariable analysis was carried out to establish the relationship of predictive factors in oncological outcomes. RESULTS: Eighty-eight (13.5%) of 654 patients developed recurrence. The mean time to recurrence was 19.8 ± 13.5 months. There were 36 (5.5%) cancer-related deaths at a mean duration of follow-up of 46.3 ± 21.6 months. Two hundred and sixty-six patients had extramural venous invasion (40.7%). EMVI was significantly associated with reduced overall recurrence-free survival, systemic recurrence-free survival, and increased cancer-related death on univariate analysis (p < 0.001 for all, Fig. 1), and multivariable analysis (OR 1.8 and 2.1 respectively, p < 0.05 for both). CONCLUSION: EMVI is associated with a poor prognosis, independent of stage, nodal status and other histopathological features. The presence of EMVI should be strongly considered as an indication for adjuvant therapy.

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AIM: In low rectal cancers without sphincter involvement a permanent stoma can be avoided without compromising oncological safety. Functional outcomes following coloanal anastomosis (CAA) compared to abdominoperineal excision (APR) may be significantly different. This study examines all available comparative quality of life (QoL) data for patients undergoing CAA versus APR for low rectal cancer. METHODS: Published studies with comparative data on QoL outcomes following CAA versus APR for low rectal cancer were extracted from electronic databases. The study was registered with PROSPERO and adhered to PRISMA (Preferred Reporting Items in Systematic Reviews and Meta-analyses) guidelines. Data was combined using random-effects models. RESULTS: Seven comparative series examined QoL in 527 patients. There was no difference in the numbers receiving neoadjuvant radiotherapy in the APR and CAA groups (OR: 1.19, 95% CI: 0.78-1.81, p = 0.43). CAA was associated with higher mean scores for physical functioning(std mean diff -7.08, 95% CI: -11.92 to -2.25, p = 0.004) and body image (std. mean diff 11.11, 95% CI: 6.04-16.18, p < 0.0001). Male sexual problems were significantly increased in patients who had undergone APR compared to CAA (std. mean diff -16.20, 95% CI: -25.76 to -6.64, p = 0.0009). Patients who had an APR reported more fatigue, dyspnoea and appetite loss. Those who had a CAA reported higher scores for both constipation and diarrhoea. DISCUSSION: It is reasonable to offer a CAA to motivated patients where oncological outcomes will not be threatened. QoL outcomes appear to be superior when intestinal continuity is maintained, and permanent stoma avoided.

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PURPOSE: Radiotherapy is being used increasingly in the treatment of prostate cancer. However, ionising radiation may confer a small risk of a radiation-induced secondary malignancy. We aim to assess the risk of rectal cancer following pelvic radiotherapy for prostate cancer. METHODS: A search was conducted of the PubMed/MEDLINE, EMBASE and Web of Science databases identifying studies reporting on the risk of rectal cancer following prostatic radiotherapy. Studies must have included an appropriate control group of non-irradiated prostate cancer patients. A meta-analysis was performed to assess the risk of prostatic radiotherapy on subsequent rectal cancer diagnosis. RESULTS: In total, 4757 articles were screened with eight studies meeting the predetermined criteria. A total of 796,386 patients were included in this meta-analysis which showed an increased odds ratio (OR) for subsequent rectal cancer in prostate cancer patients treated with radiotherapy compared to those treated by non-radiotherapy means (OR 1.45, 1.07-1.97, p = 0.02). CONCLUSION: These findings confirm that prostate radiotherapy significantly increases the risk of subsequent rectal cancer. This risk has implications for treatment selection, surveillance and patient counselling. However, it is crucial that this information is presented in a rational and comprehensible manner that does not disproportionately frighten or deter patients from what might be their most suitable treatment modality.

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Background: Rectal gastrointestinal stromal tumours (GISTs) have many treatment options, but uncertainty remains regarding the best treatment regimen for this rare pathology. The aim of this review is to assess the optimal management approach including timing of chemotherapy. Methods: PubMed, EMBASE, and Cochrane databases were searched for relevant articles comparing the impact of radical vs. local excision, and neoadjuvant vs. adjuvant therapy had on outcomes in the management of rectal GISTs. We specifically evaluated the influence that the aforementioned factors had on margins, recurrence, overall survival, 5-year disease-free survival, and hospital length of stay. Results: Twenty-eight studies met our predefined criteria and were included in our study, twelve of which were included in the quantitative synthesis. When comparing neoadjuvant versus adjuvant chemotherapy, our meta-analysis noted no significance in terms of margin negativity (R0) (odds ratio [OR] 2.01, 95% confidence interval [CI], 0.7−5.79, p = 0.20) or recurrence rates (OR 0.22, 95% CI, 0.02−1.91, p = 0.17). However, there was a difference in overall 5-year survival in favour of neoadjuvant therapy (OR 3.19, 95% CI, 1.37−7.40, * p = 0.007). Comparing local excision versus radical excision, our meta-analysis observed no significance in terms of overall 5-year survival (OR1.31, 95% CI, 0.81−2.12, p = 0.26), recurrence (OR 0.67, 95% CI, 0.40−1.13, p = 0.12), or 5-year disease-free survival (OR 1.10, 95% CI, 0.55−2.19, p = 0.80). There was a difference in length of hospital stay with a reduced mean length of stay in local excision group (mean difference [MD] 6.74 days less in the LE group; 95% CI, −6.92−−6.56, * p =< 0.00001) as well as a difference in R0 rates in favour of radical resection (OR 0.68, 95% CI, 0.47−0.99, * p = 0.05). Conclusion: Neoadjuvant chemotherapy is associated with improved overall 5-year survival, while local excision is associated with reduced mean length of hospital stay. Further large-volume, prospective studies are required to further define the optimal treatment regimen in this complex pathology.

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BACKGROUND: Acute sigmoid volvulus (ASV) represents a small but significant portion of cases of large bowel obstruction, especially in the elderly and co-morbid. Given the characteristics of the patient cohort most commonly affected, a non-operative/conservative approach is often undertaken but is associated with a high rate of recurrence. OBJECTIVE: We sought to evaluate outcomes for those patients who underwent non-operative management, emergency surgery or staged, semi-elective surgery following decompression for ASV at our institution. METHODS: Hospital in-patient enquiry (HIPE) data were used to identify all patients who presented with sigmoid volvulus between January 2005 and June 2020 inclusive. Patient notes were interrogated, including surgical and endoscopic procedures performed. Patient demographics and co-morbidities were recorded. RESULTS: Thirty-nine patients were treated over a 15-year period with a mean age of 73 years at first presentation (range 36-93). Twenty-two patients (56%) had just a single admission for ASV with three deaths in this group. Seventeen patients (44%) had more than one admission with volvulus due to recurrence after a decompression-only strategy on the index admission. Of these, three succumbed to complications of their subsequent episodes of volvulus. Twenty-five patients underwent surgical intervention (fifteen on, or shortly following, their first admission and ten following at least two admissions for ASV). The overall mortality in the operative group was 2/25 (8%) with both deaths in those undergoing emergency surgeries. Five patients were treated successfully with endoscopic measures alone and had required no further interventions at the time of compiling data. CONCLUSION: There is a high recurrence rate following non-operative management of acute sigmoid volvulus and consequently, a cumulative increase in the attendant significant morbidity and mortality with subsequent episodes. Given the relatively low complication rate of definitive surgery, even in those patients perceived to be high risk, we contend that all patients should be considered for early surgery to prevent the likely recurrence of sigmoid volvulus.

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PURPOSE: Anastomotic leak (AL) following colorectal cancer resection is associated with considerable morbidity and mortality with an impact on recurrence rates and survival. The impact of obesity on AL rates is debated. This meta-analysis aims to investigate the relationship between obesity and AL. METHODS: A search was conducted of the PubMed/MEDLINE, and Web of Science databases and included studies were split into Western and Asian groups based on population-specific body mass index (BMI) ranges for obesity. A meta-analysis was performed to assess the impact of obesity on AL rate following colorectal cancer resection. RESULTS: Two thousand three hundred and four articles were initially screened. Thirty-one studies totaling 32,953 patients were included. Patients with obesity had a statistically significant increase in AL rate in all Western and Asian study groups. However, this increase was only clinically significant in the rectal anastomotic subgroups-Western: 10.8% vs 8.4%, OR 1.57 (1.01-2.44) and Asian: 9.4% vs 7.4%, OR 1.58 (1.07-2.32). CONCLUSIONS: The findings of this analysis confirm that obesity is a significant risk factor for anastomotic leak, particularly in rectal anastomoses. This effect is thought to be primarily mediated via technical difficulties of surgery although metabolic and immunological factors may also play a role. Obesity in patients undergoing restorative CRC resection should be discussed and considered as part of the pre-operative counselling.

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Locally advanced rectal cancer is treated with neoadjuvant-chemoradiotherapy; however, only ~22% of patients achieve a complete response, and resistance mechanisms are poorly understood. The role of inflammation and immune cell biology in this setting is under-investigated. In this study, we profiled the inflammatory protein secretome of normal (non-cancer) (n = 8) and malignant rectal tissue (n = 12) pre- and post-radiation in human ex vivo explant models and examined the influence of these untreated and treated secretomes on dendritic cell biology (n = 8 for cancer and normal). These resultant profiles were correlated with patient clinical characteristics. Nineteen factors were secreted at significantly higher levels from the rectal cancer secretome when compared to the normal rectal secretome; Flt-1, P1GF, IFN-γ, IL-6, IL-10, CCL20, CCL26, CCL22, CCL3, CCL4, CCL17, GM-CSF, IL-12/IL-23p40, IL-17A, IL-1α, IL-17A/F, IL-1RA, TSLP and CXCL10 (p < 0.05). Radiation was found to have differential effects on normal rectal tissue and rectal cancer tissue with increased IL-15 and CCL22 secretion following radiation from normal rectal tissue explants (p < 0.05), while no significant alterations were observed in the irradiated rectal cancer tissue. Interestingly, however, the irradiated rectal cancer secretome induced the most potent effect on dendritic cell maturation via upregulation of CD80 and PD-L1. Patient's visceral fat area correlated with secreted factors including CCL20, suggesting that obesity status may alter the tumour microenvironment (TME). These results suggest that radiation does not have a negative effect on the ability of the rectal cancer TME to induce an immune response. Understanding these responses may unveil potential therapeutic targets to enhance radiation response and mitigate normal tissue injury. Tumour irradiation in this cohort enhances innate immune responses, which may be harnessed to improve patient treatment outcome.

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Locally advanced rectal cancer is treated with neoadjuvant-chemoradiotherapy, however only 22% of patients achieve a complete response. Resistance mechanisms are poorly understood. Radiation-induced Bystander Effect (RIBE) describes the effect of radiation on neighbouring unirradiated cells. We investigated the effects of ex vivo RIBE-induction from normal and rectal cancer tissue on bystander cell metabolism, mitochondrial function and metabolomic profiling. We correlated bystander events to patient clinical characteristics. Ex vivo RIBE-induction caused metabolic alterations in bystander cells, specifically reductions in OXPHOS following RIBE-induction in normal (p = 0.01) and cancer tissue (p = 0.03) and reduced glycolysis following RIBE-induction in cancer tissue (p = 0.01). Visceral fat area correlated with glycolysis (p = 0.02) and ATP production (p = 0.03) following exposure of cells to TCM from irradiated cancer biopsies. Leucine levels were reduced in the irradiated cancer compared to the irradiated normal secretome (p = 0.04). ROS levels were higher in cells exposed to the cancer compared to the normal secretome (p = 0.04). RIBE-induction ex vivo causes alterations in the metabolome in normal and malignant rectal tissue along with metabolic alterations in bystander cellular metabolism. This may offer greater understanding of the effects of RIBE on metabolism, mitochondrial function and the secreted metabolome.