Protocol for the CoNoR Study: A prospective multi-step study of the potential added benefit of two novel assessment tools in colorectal liver metastases technical resectability decision-making.

INTRODUCTION: Liver resection is the only curative treatment for colorectal liver metastases (CLM). Resectability decision-making is therefore a key determinant of outcomes. Wide variation has been demonstrated in resectability decision-making, despite the existence of criteria. This paper summarises a study protocol to evaluate the potential added value of two novel assessment tools in assessing CLM technical resectability: the Hepatica preoperative MR scan (MR-based volumetry, Couinaud segmentation, liver tissue characteristics and operative planning tool) and the LiMAx test (hepatic functional capacity). METHODS AND ANALYSIS: This study uses a systematic multistep approach, whereby three preparatory workstreams aid the design of the final international case-based scenario survey:Workstream 1: systematic literature review of published resectability criteria.Workstream 2: international hepatopancreatobiliary (HPB) interviews.Workstream 3: international HPB questionnaire.Workstream 4: international HPB case-based scenario survey.The primary outcome measures are change in resectability decision-making and change in planned operative strategy, resulting from the novel test results. Secondary outcome measures are variability in CLM resectability decision-making and opinions on the role for novel tools. ETHICS AND DISSEMINATION: The study protocol has been approved by a National Health Service Research Ethics Committee and registered with the Health Research Authority. Dissemination will be via international and national conferences. Manuscripts will be published. REGISTRATION DETAILS: The CoNoR Study is registered with ClinicalTrials.gov (registration number NCT04270851). The systematic review is registered on the PROSPERO database (registration number CRD42019136748).

Obesity at age 20 and weight gain during adulthood increase risk of total and premature all-cause mortality: findings from women attending breast screening in Manchester.

BACKGROUND: Obesity in early adulthood is associated with lower breast cancer rates in later life. This could be interpreted as a positive reinforcement of excess weight amongst younger women however, the wider implications of higher weights are less well known. This study examined the association between both obesity in early adulthood and body mass index (BMI) change through adulthood, and all-cause mortality. METHODS: The Predicting Risk of Cancer At Screening (PROCAS) study recruited 57,902 women aged 46-73 years (median age 57.2, IQR 51.8-63.7 years) from the Greater Manchester National Health Service breast screening programme in North West England between 2009 and 2015. It was used to assess associations between BMI at 20 years and cohort entry with all-cause mortality ascertained via deaths recorded on the National Breast Screening System to June 2020. Hazard ratios were estimated using proportional hazards (Cox) regression adjusted for factors at entry to the cohort: age, deprivation, bilateral oophorectomy, hormone-replacement therapy, menopausal status, ethnicity, alcohol intake, physical activity, and BMI. RESULTS: The prevalence of overweight (25-30 kg/m2) and obesity (> 30 kg/m2) were 10.4% and 2.5% respectively at 20 years, increasing to 35.2% and 25.9% respectively at cohort entry. After a mean 8.7 years follow-up we observed that overweight (HR = 1.27, 95%CI = 1.10-1.47) and obesity (HR = 2.11, 95%CI = 1.67-2.66) at 20 years had a higher mortality rate compared with healthy weight. Women who were underweight/healthy weight at 20 years and gained weight to obesity at entry had a slightly increased mortality rate compared with women who were underweight/healthy weight at both time points (HR 1.16, 95%CI = 1.02-1.32). Women with overweight (HR = 1.36, 95%CI = 1.06-1.75) or obesity (HR = 1.90, 95%CI = 1.45-2.48) at both 20 years and entry had a higher mortality rate than women who were underweight/healthy weight at both points. CONCLUSIONS: Women who self-reported overweight and obesity at 20 years had a shorter life expectancy in this cohort of women attending breast cancer screening. Weight gain from 20 years was common in this group. Girls and women should be supported to maintain a healthy weight throughout the lifespan to help increase life expectancy. Trial registration number NCT04359420, retrospectively registered 24/04/2020.

Age alone is not a barrier to efficacy of cytoreductive surgery and hyperthermic intraperitoneal chemotherapy for colorectal peritoneal metastases: analysis of 1138 patients from the UK and Ireland Colorectal Peritoneal Metastases Registry.

BACKGROUND: The management of colorectal peritoneal metastases continues to be a challenge but recent evidence suggests cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) can improve survival. Uncertainty about the relationship between age and tumour biology makes patient selection challenging particularly when reported procedure related morbidity is high and impact on survival outcomes unknown. The UK and Ireland Colorectal Peritoneal Metastases Registry was reviewed to assess the influence of age on efficacy of CRS and HIPEC. METHODS: A review of outcomes from the UK and Ireland Colorectal Peritoneal Metastases Registry was performed. Data from 2000 to 2021 were included from five centres in the UK and Ireland, and the cohort were sub-divided into three age groups; <45 years, 45-65 years and >65 years old. Primarily, we examined post-operative morbidity and survival outcomes across the three age groups. In addition, we examined the impact that the completeness of cytoreduction, nodal status, or adverse pathological features had on long-term survival. RESULTS: During the study period, 1138 CPM patients underwent CRS HIPEC. 202 patients(17.8%) were <45 years, 549 patients(48.2%) aged 45-65 years and 387 patients(34%) >65 years. Overall, median length of surgery (CRS and HIPEC), median PCI score and rate of HIPEC administration was similar in all three groups, as was overall rates of major morbidity and/or mortality. Complete cytoreduction rates (CC0) were similar across the three cohorts; 77%, 80.6% and 81%, respectively. Median overall survival for all patients was 38 months following complete cytoreduction. CONCLUSION: Age did not appear to influence morbidity or long-term survival following CRS and HIPEC. When complete cytoreduction is achieved survival outcomes are good. The addition of HIPEC can be performed safely and may reduce local recurrence within the peritoneum.

Patterns and Timing of Recurrence following CRS and HIPEC in Colorectal Cancer Peritoneal Metastasis.

INTRODUCTION: Cytoreductive Surgery and Hyperthermic Intraperitoneal Chemotherapy (CRS/HIPEC) is an established treatment of Colorectal Peritoneal Metastases (CRPM). This study aims to determine the timing and patterns of recurrent disease on imaging following complete CRS/HIPEC. METHODS: Retrospective analysis of a national peritoneal tumour service database identified CRPM patients with complete CRS/HIPEC(CC0) from 2005 to-2018. Patients with<2 years follow-up or and those where post-operative histology from the CRS/HIPEC procedure did not confirm CRPM from their original colorectal cancer were excluded. Time to recurrence was measured from surgery to first radiologically illustrated recurrence. CT was the primary modality used, supplemented by PET-CT or MRI if required. Outcomes of interest were survival data (including overall survival (OS), disease-free survival (DFS) and peritoneal-recurrence free survival (PRFS)), timing and patterns of recurrent disease. RESULTS: 146 of the 176 patients identified were eligible for inclusion. Median OS for all study patients was 45.2 months (95% CI 38-53 months), median DFS was 11.7 months (95% CI 9-14 months), and median PRFS was 25.2 months (95% CI 14.7-30 months). Recurrent disease was seen in 112 cases (77%), radiologically classified as intraperitoneal in 50 patients (44%), single site systemic in 21 patients (19%) and multi-site in 41 patients (37%). CT detection rate for disease recurrence was 88%. Subgroup analyses showed that PCI ≥12, positive nodal primary disease and synchronous peritoneal disease were associated with worse outcomes. CONCLUSION: Patients selected for CRS/HIPEC for CRPM have an OS > 45 months, with the majority recurring systemically within a year. Peritoneal recurrence is a later event after several years. Surveillance programs in this group should be most intensive in the first 2 years after surgery, using CT with oral and intravenous contrast.

Clinical and radiomics prediction of complete response in rectal cancer pre-chemoradiotherapy.

Background and purpose: Patients with rectal cancer could avoid major surgery if they achieve clinical complete response (cCR) post neoadjuvant treatment. Therefore, prediction of treatment outcomes before treatment has become necessary to select the best neo-adjuvant treatment option. This study investigates clinical and radiomics variables' ability to predict cCR in patients pre chemoradiotherapy. Materials and methods: Using the OnCoRe database, we recruited a matched cohort of 304 patients (152 with cCR; 152 without cCR) deriving training (N = 200) and validation (N = 104) sets. We collected pre-treatment MR (magnetic resonance) images, demographics and blood parameters (haemoglobin, neutrophil, lymphocyte, alkaline phosphate and albumin). We segmented the gross tumour volume on T2 Weighted MR Images and extracted 1430 stable radiomics features per patient. We used principal component analysis (PCA) and receiver operating characteristic area under the curve (ROC AUC) to reduce dimensionality and evaluate the models produced. Results: Using Logistic regression analysis, PCA-derived combined model (radiomics plus clinical variables) gave a ROC AUC of 0.76 (95% CI: 0.69-0.83) in the training set and 0.68 (95% CI 0.57-0.79) in the validation set. The clinical only model achieved an AUC of 0.73 (95% CI 0.66-0.80) and 0.62 (95% CI 0.51-0.74) in the training and validation set, respectively. The radiomics model had an AUC of 0.68 (95% CI 0.61-0.75) and 0.66 (95% CI 0.56-0.77) in the training and validation sets. Conclusion: The predictive characteristics of both clinical and radiomics variables for clinical complete response remain modest but radiomics predictability is improved with addition of clinical variables.

Establishing a colorectal cancer research database from routinely collected health data: the process and potential from a pilot study.

OBJECTIVE: Colorectal cancer is a common cause of death and morbidity. A significant amount of data are routinely collected during patient treatment, but they are not generally available for research. The National Institute for Health Research Health Informatics Collaborative in the UK is developing infrastructure to enable routinely collected data to be used for collaborative, cross-centre research. This paper presents an overview of the process for collating colorectal cancer data and explores the potential of using this data source. METHODS: Clinical data were collected from three pilot Trusts, standardised and collated. Not all data were collected in a readily extractable format for research. Natural language processing (NLP) was used to extract relevant information from pseudonymised imaging and histopathology reports. Combining data from many sources allowed reconstruction of longitudinal histories for each patient that could be presented graphically. RESULTS: Three pilot Trusts submitted data, covering 12 903 patients with a diagnosis of colorectal cancer since 2012, with NLP implemented for 4150 patients. Timelines showing individual patient longitudinal history can be grouped into common treatment patterns, visually presenting clusters and outliers for analysis. Difficulties and gaps in data sources have been identified and addressed. DISCUSSION: Algorithms for analysing routinely collected data from a wide range of sites and sources have been developed and refined to provide a rich data set that will be used to better understand the natural history, treatment variation and optimal management of colorectal cancer. CONCLUSION: The data set has great potential to facilitate research into colorectal cancer.

Prospective study of change in liver function and fat in patients with colorectal liver metastases undergoing preoperative chemotherapy: protocol for the CLiFF Study.

INTRODUCTION: Preoperative chemotherapy in patients undergoing resection for colorectal liver metastases (CLM) improves oncological outcomes. However, chemotherapy-associated liver injury (occurring in two patterns: vascular and fat deposition) is a real clinical concern prior to hepatic resection. After major liver resection, regeneration of the residual liver is a prerequisite for recovery and avoidance of liver failure, but this regenerative capacity may be hindered by chemotherapy. Thus, there is a need to predict for this serious complication. Over the past two decades, several tests and derived indices have been developed, which have failed to achieve clinical utility, mainly as they were indirect measurements of liver function. Here, we will use a novel test of liver function (the liver maximum capacity (LiMAx) test), and measure liver fat using MRI. METHODS AND ANALYSIS: This prospective study will assess changes in liver function longitudinally, measured by the LiMAx test, and liver fat, measured by advanced MRI using both MR spectroscopy and the modified Dixon method, in up to 35 patients undergoing preoperative chemotherapy for CLM. The primary outcomes will be the changes in liver function and fat compared with baseline prechemotherapy measurements. Secondary outcome measures include: routinely measured liver function blood tests, anthropometric measurements, postoperative histology and digital quantification of fat, postoperative complications and mortality and quality of life. ETHICS AND DISSEMINATION: The study was approved by a National Health Service Research Ethics Committee and registered with the Health Research Authority. Dissemination will be via international and national conferences and the National Institute for Health Research network. Manuscripts will be published. TRIAL REGISTRATION NUMBER: This study is registered online at www.clinicaltrials.gov (registration number NCT03562234).

Temporal improvements in loco-regional failure and survival in patients with anal cancer treated with chemo-radiotherapy: treatment cohort study (1990-2014).

BACKGROUND: We evaluated oncological changes in patients with squamous cell carcinoma of the anus (SCCA) treated by chemoradiotherapy (CRT) from a large UK institute, to derive estimates of contemporary outcomes. METHODS: We performed a treatment-cohort analysis in 560 patients with non-metastatic SCCA treated with CRT over 25 years. The primary outcomes were 3-year loco-regional failure (LRF), 5-year overall survival (OS), and 5-year cancer-specific survival (CSS). We developed prediction models; and overlaid estimates on published results from historic trials. RESULTS: Age distributions, proportions by gender and cT stage remained stable over time. The median follow-up was 61 (IQR: 36-79) months. Comparing the first period (1990-1994) with the last period (2010-2014), 3-year LRF declined from 33 to 16% (Ptrends < 0.001); 5-year OS increased from 60% to 76% (Ptrends = 0.001); and 5-year CCS increased from 62% in to 80% (Ptrends = 0.001). For 2020, the models predicted a 3-year LRF of 14.7% (95% CIs: 0-31.3); 5-year OS of 74.7% (95% CIs: 54.6-94.9); and 5-year CSS of 85.7% (95% CIs: 75.3-96.0). Reported oncological outcomes from historic trials generally underestimated contemporary outcomes. CONCLUSIONS: Current and predicted rates for 3-year LRF and 5-year survivals are considerably improved compared with those in historic trials.

Quality optimisation in colonoscopy: a function of time of colonoscopy or bowel preparation.

To test the hypothesis claimed in recent studies that quality of bowel preparation for colonoscopy could be influenced by the time of the day colonoscopy is performed. Do patients in morning list have better bowel preparation than those on the afternoon list? Retrospective analysis of 736 consecutive patients who had colonoscopy from 1st August to 31st December 2012. Patients with poor bowel preparation (Boston Bowel Prep Score 6 or less) were identified (n = 242). Colonoscopy reports of these patients analysed. Patients were stratified into two groups (am and pm) and results compared. Mean patient age 63.9 years (range 19-89). Male to female ratio 1:1. 92% of patients were given Moviprep. for bowel preparation. 32.9% (242/736) of patients were identified as having inadequate bowel preparation. 37.7% of morning list patients had poor bowel preparation. 26.7% of afternoon list patients had poor bowel preparation. 14.7% (108/736) had incomplete colonoscopy, of which 26.9% (29/108) were due to poor bowel preparation. The commonest reasons for incomplete examination were patient discomfort & bowel looping. Our study demonstrates that morning session patients had poorer bowel preparation than the afternoon session patients in contrast to published evidence in recent literature. This implies that timing of bowel preparation is probably more important than timing of colonoscopy. Poor bowel preparation does not seem to have a significant impact on the colonoscopy failure rate in this series.

Factors affecting local regrowth after watch and wait for patients with a clinical complete response following chemoradiotherapy in rectal cancer (InterCoRe consortium): an individual participant data meta-analysis.

BACKGROUND: In patients with rectal cancer who achieve clinical complete response after neoadjuvant chemoradiotherapy, watch and wait is a novel management strategy with potential to avoid major surgery. Study-level meta-analyses have reported wide variation in the proportion of patients with local regrowth. We did an individual participant data meta-analysis to investigate factors affecting occurrence of local regrowth. METHODS: We updated search results of a recent systematic review by searching MEDLINE and Embase from Jan 1, 2016, to May 5, 2017, and used expert knowledge to identify published studies reporting on local regrowth in patients with rectal cancer managed by watch and wait after clinical complete response to neoadjuvant chemoradiotherapy. We restricted studies to those that defined clinical complete response using criteria equivalent to São Paulo benchmarks (ie, absence of residual ulceration, stenosis, or mass within the rectum on clinical and endoscopic examination). The primary outcome was 2-year cumulative incidence of local regrowth, estimated with a two-stage random-effects individual participant data meta-analysis. We assessed the effects of clinical and treatment factors using Cox frailty models, expressed as hazard ratios (HRs). From these models, we derived percentage differences in mean θ as an approximation of the effect of measured covariates on between-centre heterogeneity. This study is registered with PROSPERO, number CRD42017070934. FINDINGS: We obtained individual participant data from 11 studies, including 602 patients enrolled between March 11, 1990, and Feb 13, 2017, with a median follow-up of 37·6 months (IQR 25·0-58·7). Ten of the 11 datasets were judged to be at low risk of bias. 2-year cumulative incidence of local regrowth was 21·4% (random-effects 95% CI 15·3-27·6), with high levels of between-study heterogeneity (I2=61%). We noted wide between-centre variation in patient, tumour, and treatment characteristics. We found some evidence that increasing cT stage was associated with increased risk of local regrowth (random-effects HR per cT stage 1·40, 95% CI 1·00-1·94; ptrend=0·048). In a subgroup of 459 patients managed after 2008 (when pretreatment staging by MRI became standard), 2-year cumulative incidence of local regrowth was 19% (95% CI 13-28) for stage cT1 and cT2 tumours, 31% (26-37) for cT3, and 37% (21-60) for cT4 (random-effects HR per cT stage 1·50, random-effects 95% CI 1·03-2·17; ptrend=0·0330). We estimated that measured factors contributed 4·8-45·3% of observed between-centre heterogeneity. INTERPRETATION: In patients with rectal cancer and clinical complete response after chemoradiotherapy managed by watch and wait, we found some evidence that increasing cT stage predicts for local regrowth. These data will inform clinician-patient decision making in this setting. Research is needed to determine other predictors of a sustained clinical complete response. FUNDING: None.

Long-term Quality of Life After Cytoreductive Surgery and Heated Intraperitoneal Chemotherapy for Pseudomyxoma Peritonei: A Prospective Longitudinal Study.

BACKGROUND: Cytoreductive surgery (CRS) and hyperthermic intraperitoneal chemotherapy (HIPEC) are an established treatment for pseudomyxoma peritonei (PMP), but it is a major surgical procedure and may be associated with long-term morbidity. To date, health-related quality-of-life (HRQL) data among survivors are lacking. METHODS: A two-period qualitative study investigated patients undergoing CRS-HIPEC for PMP at a national peritoneal tumor center between 2003 and 2011. First, the European Organization for Research and Treatment (EORTC)-QLQ C30 HRQL questionnaire was used longitudinally preoperatively and at postoperative months 3, 6, 9, 12, 18, and 24, then yearly thereafter. Second, it was updated in 2016 as a cross-sectional study. Both studies were compared with age- and sex-matched reference populations (one-way t tests). RESULTS: A total of 553 longitudinal HRQL questionnaires were completed for 137 patients, truncated at 60 months. In the 2016 update, 85 responses were received from 103 survivors (mean follow-up period, 8.11 years). Patients' physical, role, and social function scores were impaired until 12 months postoperatively, after which the scores did not differ significantly from those of with reference populations. Similarly, fatigue, appetite loss, insomnia, and financial difficulties worsened significantly compared with reference populations in the first 12-months and then normalized. In contrast, impaired cognitive function (82.3 vs 88.5; P = 0.017), constipation (13.7 vs 7.3; P = 0.032), and diarrheal symptoms (15.1 vs 4.9; P = 0.0006) persisted through both periods. Global health scores did not differ significantly from those of the reference population. CONCLUSIONS: Beyond 12 months postoperatively, CRS-HIPEC for PMP is associated with a good quality of life except for some cognitive functional impairment and bowel disturbances.

Defunctioning stoma- a prognosticator for leaks in low rectal restorative cancer resection: A retrospective analysis of stoma database.

AIMS: Low anterior resection (LAR) has higher risk of anastomotic leak with its attendant morbidity -mortality. De-functioning loop ileostomy (DLI), claimed to mitigate the consequences of anastomotic leak, has been questioned in recent years. This study aims to evaluate the impact of ileostomy on LAR. METHODS: A retrospective analysis of stoma database. 136 patients with stoma (March 2011-July 2015) were assessed. Data was analysed in respect to LAR anastomotic leak rate, impact on morbidity-mortality, short and long-term stoma complications, rate of ileostomy reversal and reasons for non-reversal. RESULTS: 45 patients had loop ileostomy for LAR. Male (28) to female (17) ratio was 1.65:1 with median age of 69 (IQR: 56-75.5). Only 3 anastomotic leaks (3/45, 6.5%) occurred, all treated conservatively with no mortality. 29 had reversal, average reversal time is 10 months (3-24) and 5 awaiting. Reasons for non-reversal included patients' choice (7), death from cardiac cause (1), chemotherapy (1), unfit for surgery (1) and failed reversal (1). Acute complications included high output & reversible AKI (1), bleeding (3) and minor complications (6) as skin excoriation, separation and appliance issues. Parastomal hernia was repaired during reversal (12/15). CONCLUSIONS: De-functioning ileostomy for LAR is a safe procedure with low morbidity. Most stomas are reversible. Series highlights a late reversal contrary to the nationally recommended guidelines. Most interestingly, the study demonstrated de-functioning mitigated clinical consequences of anastomotic leak to an extent that reoperation was avoidable, in keeping with recent meta-analysis indicating a significantly low anastomotic leakage rates and reoperation. Larger study is invaluable to substantiate findings.

Nodal stage migration and prognosis in anal cancer: a systematic review, meta-regression, and simulation study.

BACKGROUND: In patients with squamous cell carcinoma of the anus (SCCA), lymph node positivity (LNP) indicates poor prognosis for survival and is central to radiotherapy planning. Over the past three decades, LNP proportion has increased, mainly reflecting enhanced detection with newer imaging modalities; a process known as nodal stage migration. If accompanied by constant T stage distributions, prognosis for both lymph node-positive and lymph node-negative groups may improve without any increase in overall survival for individual patients; a paradox termed the Will Rogers phenomenon. Here, we aim to systematically evaluate the impact of nodal stage migration on survival in SCCA and address a novel hypothesis that this phenomenon results in reduced prognostic discrimination. METHODS: We did a systematic review and meta-regression to quantify changes in LNP over time and the impact of this change on survival and prognostic discrimination. We searched MEDLINE, Embase, and the Cochrane Library to identify randomised trials and observational studies in patients with SCCA published between Jan 1, 1970, and Oct 11, 2016. Studies were eligible if patients received chemoradiotherapy or radiotherapy as the main treatment, reported LNP proportions (all studies), and reported overall survival (not necessarily present in all studies). We excluded studies with fewer than 50 patients. We extracted study-level data with a standardised, piloted form. The primary outcome measure was 5-year overall survival. To investigate scenarios in which reduced prognostic discrimination might occur, we simulated varying true LNP proportions and true overall survival, and compared these with expected observed outcomes for varying levels of misclassification of true nodal state. FINDINGS: We identified 62 studies reporting LNP proportions, which included 10 569 patients. From these, we included 45 studies (6302 patients) with whole cohort 5-year overall survival, 11 studies with 5-year survival stratified by nodal status, and 20 studies with hazard ratios in our analyses of temporal changes. In 62 studies, the LNP proportions increased from a mean estimate of 15·3% (95% CI 10·5-20·1) in 1980 to 37·1% (34·0-41·3) in 2012 (p<0·0001). In 11 studies with prognostic data, increasing LNP was associated with improved overall survival in both lymph node-positive and lymph node-negative categories, whereas the proportions with combined tumour stage T3 and T4 remained constant. In 20 studies, across a range of LNP proportions from 15% to 40%, the hazard ratios for overall survival of lymph node-positive versus lymph node-negative patients decreased significantly from 2·5 (95% CI 1·8-3·3) at 15% LNP to 1·3 (1·2-1·9; p=0·014) at 40% LNP. The simulated scenarios reproduced this effect if the true LNP proportions were 20% or 25%, but not if the true LNP proportions were 30% or greater. INTERPRETATION: We describe a consequence of staging misclassification in anal cancer that we have termed reduced prognostic discrimination. We used this new observation to infer that the LNP proportions of more than 30% seen in modern clinical series (11 out of 15 studies with a median year since 2007) are higher than the true LNP proportion. The introduction of new staging technologies in oncology might misclassify true disease stage, spuriously informing disease management and ultimately increasing the risk of overtreatment. FUNDING: Bowel Disease Research Foundation.

Watch-and-wait approach versus surgical resection after chemoradiotherapy for patients with rectal cancer (the OnCoRe project): a propensity-score matched cohort analysis.

BACKGROUND: Induction of a clinical complete response with chemoradiotherapy, followed by observation via a watch-and-wait approach, has emerged as a management option for patients with rectal cancer. We aimed to address the shortage of evidence regarding the safety of the watch-and-wait approach by comparing oncological outcomes between patients managed by watch and wait who achieved a clinical complete response and those who had surgical resection (standard care). METHODS: Oncological Outcomes after Clinical Complete Response in Patients with Rectal Cancer (OnCoRe) was a propensity-score matched cohort analysis study, that included patients of all ages diagnosed with rectal adenocarcinoma without distant metastases who had received preoperative chemoradiotherapy (45 Gy in 25 daily fractions with concurrent fluoropyrimidine-based chemotherapy) at a tertiary cancer centre in Manchester, UK, between Jan 14, 2011, and April 15, 2013. Patients who had a clinical complete response were offered management with the watch-and-wait approach, and patients who did not have a complete clinical response were offered surgical resection if eligible. We also included patients with a clinical complete response managed by watch and wait between March 10, 2005, and Jan 21, 2015, across three neighbouring UK regional cancer centres, whose details were obtained through a registry. For comparative analyses, we derived one-to-one paired cohorts of watch and wait versus surgical resection using propensity-score matching (including T stage, age, and performance status). The primary endpoint was non-regrowth disease-free survival from the date that chemoradiotherapy was started, and secondary endpoints were overall survival, and colostomy-free survival. We used a conservative p value of less than 0·01 to indicate statistical significance in the comparative analyses. FINDINGS: 259 patients were included in our Manchester tertiary cancer centre cohort, 228 of whom underwent surgical resection at referring hospitals and 31 of whom had a clinical complete response, managed by watch and wait. A further 98 patients were added to the watch-and-wait group via the registry. Of the 129 patients managed by watch and wait (median follow-up 33 months [IQR 19-43]), 44 (34%) had local regrowths (3-year actuarial rate 38% [95% CI 30-48]); 36 (88%) of 41 patients with non-metastatic local regrowths were salvaged. In the matched analyses (109 patients in each treatment group), no differences in 3-year non-regrowth disease-free survival were noted between watch and wait and surgical resection (88% [95% CI 75-94] with watch and wait vs 78% [63-87] with surgical resection; time-varying p=0·043). Similarly, no difference in 3-year overall survival was noted (96% [88-98] vs 87% [77-93]; time-varying p=0·024). By contrast, patients managed by watch and wait had significantly better 3-year colostomy-free survival than did those who had surgical resection (74% [95% CI 64-82] vs 47% [37-57]; hazard ratio 0·445 [95% CI 0·31-0·63; p<0·0001), with a 26% (95% CI 13-39) absolute difference in patients who avoided permanent colostomy at 3 years between treatment groups. INTERPRETATION: A substantial proportion of patients with rectal cancer managed by watch and wait avoided major surgery and averted permanent colostomy without loss of oncological safety at 3 years. These findings should inform decision making at the outset of chemoradiotherapy. FUNDING: Bowel Disease Research Foundation.