Decade-long leukaemia remissions with persistence of CD4+ CAR T cells.

The adoptive transfer of T lymphocytes reprogrammed to target tumour cells has demonstrated potential for treatment of various cancers1-7. However, little is known about the long-term potential and clonal stability of the infused cells. Here we studied long-lasting CD19-redirected chimeric antigen receptor (CAR) T cells in two patients with chronic lymphocytic leukaemia1-4 who achieved a complete remission in 2010. CAR T cells remained detectable more than ten years after infusion, with sustained remission in both patients. Notably, a highly activated CD4+ population emerged in both patients, dominating the CAR T cell population at the later time points. This transition was reflected in the stabilization of the clonal make-up of CAR T cells with a repertoire dominated by a small number of clones. Single-cell profiling demonstrated that these long-persisting CD4+ CAR T cells exhibited cytotoxic characteristics along with ongoing functional activation and proliferation. In addition, longitudinal profiling revealed a population of gamma delta CAR T cells that prominently expanded in one patient concomitant with CD8+ CAR T cells during the initial response phase. Our identification and characterization of these unexpected CAR T cell populations provide novel insight into the CAR T cell characteristics associated with anti-cancer response and long-term remission in leukaemia.

Disruption of TET2 promotes the therapeutic efficacy of CD19-targeted T cells.

Cancer immunotherapy based on genetically redirecting T cells has been used successfully to treat B cell malignancies1-3. In this strategy, the T cell genome is modified by integration of viral vectors or transposons encoding chimaeric antigen receptors (CARs) that direct tumour cell killing. However, this approach is often limited by the extent of expansion and persistence of CAR T cells4,5. Here we report mechanistic insights from studies of a patient with chronic lymphocytic leukaemia treated with CAR T cells targeting the CD19 protein. Following infusion of CAR T cells, anti-tumour activity was evident in the peripheral blood, lymph nodes and bone marrow; this activity was accompanied by complete remission. Unexpectedly, at the peak of the response, 94% of CAR T cells originated from a single clone in which lentiviral vector-mediated insertion of the CAR transgene disrupted the methylcytosine dioxygenase TET2 gene. Further analysis revealed a hypomorphic mutation in this patient's second TET2 allele. TET2-disrupted CAR T cells exhibited an epigenetic profile consistent with altered T cell differentiation and, at the peak of expansion, displayed a central memory phenotype. Experimental knockdown of TET2 recapitulated the potency-enhancing effect of TET2 dysfunction in this patient's CAR T cells. These findings suggest that the progeny of a single CAR T cell induced leukaemia remission and that TET2 modification may be useful for improving immunotherapies.

Two cases of severe pulmonary toxicity from highly active mesothelin-directed CAR T cells.

Multiple clinical studies have treated mesothelin (MSLN)-positive solid tumors by administering MSLN-directed chimeric antigen receptor (CAR) T cells. Although these products are generally safe, efficacy is limited. Therefore, we generated and characterized a potent, fully human anti-MSLN CAR. In a phase 1 dose-escalation study of patients with solid tumors, we observed two cases of severe pulmonary toxicity following intravenous infusion of this product in the high-dose cohort (1-3 × 108 T cells per m2). Both patients demonstrated progressive hypoxemia within 48 h of infusion with clinical and laboratory findings consistent with cytokine release syndrome. One patient ultimately progressed to grade 5 respiratory failure. An autopsy revealed acute lung injury, extensive T cell infiltration, and accumulation of CAR T cells in the lungs. RNA and protein detection techniques confirmed low levels of MSLN expression by benign pulmonary epithelial cells in affected lung and lung samples obtained from other inflammatory or fibrotic conditions, indicating that pulmonary pneumocyte and not pleural expression of mesothelin may lead to dose-limiting toxicity. We suggest patient enrollment criteria and dosing regimens of MSLN-directed therapies consider the possibility of dynamic expression of mesothelin in benign lung with a special concern for patients with underlying inflammatory or fibrotic conditions.

Assessing the learning curve of robot-assisted total mesorectal excision: a multicenter study considering procedural safety, pathological safety, and efficiency.

PURPOSE: Evidence regarding the learning curve of robot-assisted total mesorectal excision is scarce and of low quality. Case-mix is mostly not taken into account, and learning curves are based on operative time, while preferably clinical outcomes and literature-based limits should be used. Therefore, this study aims to assess the learning curve of robot-assisted total mesorectal excision. METHODS: A retrospective study was performed in four Dutch centers. The primary aim was to assess the safety of the individual and institutional learning curves using a RA-CUSUM analysis based on intraoperative complications, major postoperative complications, and compound pathological outcome (positive circumferential margin or incomplete TME specimen). The learning curve for efficiency was assessed using a LC-CUSUM analysis for operative time. Outcomes of patients before and after the learning curve were compared. RESULTS: In this study, seven participating surgeons performed robot-assisted total mesorectal excisions in 531 patients. Learning curves for intraoperative complications, postoperative complications, and compound pathological outcome did not exceed predefined literature-based limits. The LC-CUSUM for operative time showed lengths of the learning curve ranging from 12 to 35 cases. Intraoperative, postoperative, and pathological outcomes did not differ between patients operated during and after the learning curve. CONCLUSION: The learning curve of robot-assisted total mesorectal excision based on intraoperative complications, postoperative complications, and compound pathological outcome did not exceed predefined limits and is therefore suggested to be safe. Using operative time as a surrogate for efficiency, the learning curve is estimated to be between 12 and 35 procedures.

A cellular antidote to specifically deplete anti-CD19 chimeric antigen receptor-positive cells.

Unintentional transduction of B-cell acute lymphoblastic leukemia blasts during CART19 manufacturing can lead to CAR19+ leukemic cells (CARB19) that are resistant to CART19 killing. We developed an anti-CAR19 idiotype chimeric antigen receptor (αCAR19) to specifically recognize CAR19+ cells. αCAR19 CAR T cells efficiently lysed CARB19 cells in vitro and in a primary leukemia-derived xenograft model. We further showed that αCAR19-CART cells could be used as an "antidote" to deplete CART19 cells to reduce long-term side effects, such as B-cell aplasia.

Neoadjuvant FOLFOXIRI prior to chemoradiotherapy for high-risk ("ugly") locally advanced rectal cancer: study protocol of a single-arm, multicentre, open-label, phase II trial (MEND-IT).

BACKGROUND: The presence of mesorectal fascia (MRF) invasion, grade 4 extramural venous invasion (EMVI), tumour deposits (TD) or extensive or bilateral extramesorectal (lateral) lymph nodes (LLN) on MRI has been suggested to identify patients with indisputable, extensive locally advanced rectal cancer (LARC), at high risk of treatment failure. The aim of this study is to evaluate whether or not intensified chemotherapy prior to neoadjuvant chemoradiotherapy improves the complete response (CR) rate in these patients. METHODS: This multicentre, single-arm, open-label, phase II trial will include 128 patients with non-metastatic high-risk LARC (hr-LARC), fit for triplet chemotherapy. To ensure a study population with indisputable, unfavourable prognostic characteristics, hr-LARC is defined as LARC with on baseline MRI at least one of the following characteristics; MRF invasion, EMVI grade 4, enlarged bilateral or extensive LLN at high risk of an incomplete resection, or TD. Exclusion criteria are the presence of a homozygous DPD deficiency, distant metastases, any chemotherapy within the past 6 months, previous radiotherapy within the pelvic area precluding standard chemoradiotherapy, and any contraindication for the planned treatment. All patients will be planned for six two-weekly cycles of FOLFOXIRI (5-fluorouracil, leucovorin, oxaliplatin and irinotecan) prior to chemoradiotherapy (25 × 2 Gy or 28 × 1.8 Gy with concomitant capecitabine). A resection will be performed following radiological confirmation of resectable disease after the completion of chemoradiotherapy. A watch and wait strategy is allowed in case of a clinical complete response. The primary endpoint is the CR rate, described as a pathological CR or a sustained clinical CR one year after chemoradiotherapy. The main secondary objectives are long-term oncological outcomes, radiological and pathological response, the number of resections with clear margins, treatment-related toxicity, perioperative complications, health-related costs, and quality of life. DISCUSSION: This trial protocol describes the MEND-IT study. The MEND-IT study aims to evaluate the CR rate after intensified chemotherapy prior to concomitant chemoradiotherapy in a homogeneous group of patients with locally advanced rectal cancer and indisputably unfavourable characteristics, defined as hr-LARC, in order to improve their prognosis. TRIAL REGISTRATION: Clinicaltrials.gov: NCT04838496 , registered on 02-04-2021 Netherlands Trial Register: NL9790. PROTOCOL VERSION: Version 3 dd 11-4-2022.

Local recurrence of robot-assisted total mesorectal excision: a multicentre cohort study evaluating the initial cases.

PURPOSE: Evidence regarding local recurrence rates in the initial cases after implementation of robot-assisted total mesorectal excision is limited. This study aims to describe local recurrence rates in four large Dutch centres during their initial cases. METHODS: Four large Dutch centres started with the implementation of robot-assisted total mesorectal excision in respectively 2011, 2012, 2015, and 2016. Patients who underwent robot-assisted total mesorectal excision with curative intent in an elective setting for rectal carcinoma defined according to the sigmoid take-off were included. Overall survival, disease-free survival, systemic recurrence, and local recurrence were assessed at 3 years postoperatively. Subsequently, outcomes between the initial 10 cases, cases 11-40, and the subsequent cases per surgeon were compared using Cox regression analysis. RESULTS: In total, 531 patients were included. Median follow-up time was 32 months (IQR: 19-50]. During the initial 10 cases, overall survival was 89.5%, disease-free survival was 73.1%, and local recurrence was 4.9%. During cases 11-40, this was 87.7%, 74.1%, and 6.6% respectively. Multivariable Cox regression did not reveal differences in local recurrence between the different case groups. CONCLUSION: Local recurrence rate during the initial phases of implantation of robot-assisted total mesorectal procedures is low. Implementation of the robot-assisted technique can safely be performed, without additional cases of local recurrence during the initial cases, if performed by surgeons experienced in laparoscopic rectal cancer surgery.

Mechanisms of resistance to CAR T cell therapies.

Chimeric antigen receptor (CAR)-engineered T cells have demonstrated remarkable success in the treatment of B cell malignancies. FDA approval of these therapies represents a watershed moment in the development of therapies for cancer. Despite the successes of the last decade, many patients will unfortunately not experience durable responses to CAR therapy. Emerging research has shed light on the biology responsible for these failures, and further highlighted the hurdles to broader success. Here, we review the recent research identifying how interactions between cancer cells and engineered immune cells result in resistance to CAR therapies.

Chronic lymphocytic leukemia cells impair mitochondrial fitness in CD8+ T cells and impede CAR T-cell efficacy.

In chronic lymphocytic leukemia (CLL), acquired T-cell dysfunction impedes development of effective immunotherapeutic strategies, through as-yet unresolved mechanisms. We have previously shown that CD8+ T cells in CLL exhibit impaired activation and reduced glucose uptake after stimulation. CD8+ T cells in CLL patients are chronically exposed to leukemic B cells, which potentially impacts metabolic homeostasis resulting in aberrant metabolic reprogramming upon stimulation. Here, we report that resting CD8+ T cells in CLL have reduced intracellular glucose transporter 1 (GLUT1) reserves, and have an altered mitochondrial metabolic profile as displayed by increased mitochondrial respiration, membrane potential, and levels of reactive oxygen species. This coincided with decreased levels of peroxisome proliferator-activated receptor γ coactivator 1-α, and in line with that, CLL-derived CD8+ T cells showed impaired mitochondrial biogenesis upon stimulation. In search of a therapeutic correlate of these findings, we analyzed mitochondrial biogenesis in CD19-directed chimeric antigen receptor (CAR) CD8+ T cells prior to infusion in CLL patients (who were enrolled in NCT01747486 and NCT01029366 [https://clinicaltrials.gov]). Interestingly, in cases with a subsequent complete response, the infused CD8+ CAR T cells had increased mitochondrial mass compared with nonresponders, which positively correlated with the expansion and persistence of CAR T cells. Our findings demonstrate that GLUT1 reserves and mitochondrial fitness of CD8+ T cells are impaired in CLL. Therefore, boosting mitochondrial biogenesis in CAR T cells might improve the efficacy of CAR T-cell therapy and other emerging cellular immunotherapies.

Dual Targeting of Mesothelin and CD19 with Chimeric Antigen Receptor-Modified T Cells in Patients with Metastatic Pancreatic Cancer.

B cells infiltrate pancreatic ductal adenocarcinoma (PDAC) and in preclinical cancer models, can suppress T cell immunosurveillance in cancer. Here, we conducted a pilot study to assess the safety and feasibility of administering lentiviral-transduced chimeric antigen receptor (CAR)-modified autologous T cells redirected against mesothelin to target tumor cells along with CART cells redirected against CD19 to deplete B cells. Both CARs contained 4-1BB and CD3ζ signaling domains. Three patients with chemotherapy-refractory PDAC received 1.5 g/m2 cyclophosphamide prior to separate infusions of lentiviral-transduced T cells engineered to express chimeric anti-mesothelin immunoreceptor SS1 (CART-Meso, 3 × 107/m2) and chimeric anti-CD19 immunoreceptor (CART-19, 3 × 107/m2). Treatment was well tolerated without dose-limiting toxicities. Best response was stable disease (1 of 3 patients). CART-19 (compared to CART-Meso) cells showed the greatest expansion in the blood, although persistence was transient. B cells were successfully depleted in all subjects, became undetectable by 7-10 days post-infusion, and remained undetectable for at least 28 days. Together, concomitant delivery of CART-Meso and CART-19 cells in patients with PDAC is safe. CART-19 cells deplete normal B cells but at the dose tested in these 3 subjects did not improve CART-Meso cell persistence.

Nonviral RNA chimeric antigen receptor-modified T cells in patients with Hodgkin lymphoma.

Chimeric antigen receptor (CAR)-modified T cells are being investigated in many settings, including classical Hodgkin lymphoma (cHL). The unique biology of cHL, characterized by scant Hodgkin and Reed-Sternberg (HRS) cells within an immunosuppressive tumor microenvironment (TME), may pose challenges for cellular therapies directly targeting antigens expressed on HRS cells. We hypothesized that eradicating CD19+ B cells within the TME and the putative circulating CD19+ HRS clonotypic cells using anti-CD19-directed CAR-modified T cells (CART19) may indirectly affect HRS cells, which do not express CD19. Here we describe our pilot trial using CART19 in patients with relapsed or refractory cHL. To limit potential toxicities, we used nonviral RNA CART19 cells, which are expected to express CAR protein for only a few days, as opposed to CART19 generated by viral vector transduction, which expand in vivo and retain CAR expression. All 5 enrolled patients underwent successful manufacturing of nonviral RNA CART19, and 4 were infused with protocol-specified cell dose. There were no severe toxicities. Responses were seen, but these were transient. To our knowledge, this is the first CART19 clinical trial to use nonviral RNA gene delivery. This trial was registered at www.clinicaltrials.gov as #NCT02277522 (adult) and #NCT02624258 (pediatric).

The effect of the number of active electrode poles during tined lead placement on long-term efficacy of sacral neuromodulation in patients with faecal incontinence.

AIM: There is an ongoing debate as to whether or not the efficacy of sacral neuromodulation (SNM) is optimized by maximizing the total number of active electrode poles (AEPs) during lead placement because there are more programming options. However, this is at the cost of increased operating time. The aims of this study were to establish if a higher number of AEPs improves SNM efficacy during the trial period and after permanent implantable pulse generator (IPG) placement and if there is there a correlation between number of AEPs and battery life of the first placed IPG. METHOD: This was a single centre retrospective cohort study of new patients with faecal incontinence who underwent SNM between 2000 and 2018. Exclusion criteria were sphincter defect > 30%, rectocele/enterocele Grade 3 or higher and incomplete records. RESULTS: In all, 288/456 (63%) patients (women 91%; mean age 58.5 ± 11.7 years) were eligible for analysis. The number of AEPs during lead placement was two (n = 42, 14.5%), three (n = 82, 28.5%) and four (n = 164, 57%). There was no association between the number of AEPs during tined lead placement and long-term efficacy. Neither the success rate of the trial phase nor the battery life after first placed IPG was influenced by the number of AEPs. CONCLUSION: In this study, the number of AEPs does not seem to influence long-term efficacy of SNM success rate during the trial phase or the battery life of the first placed IPG. However, we also suggest that at the very least there should be two AEPs at lead placement.

The low anterior resection syndrome in a reference population: prevalence and predictive factors in the Netherlands.

AIM: The low anterior resection syndrome (LARS) severely affects quality of life (QoL) after colorectal cancer surgery. There are no data about these complaints and the association with QoL in a reference population. The aim of this study was to assess LARS and the association with QoL in a reference population. METHODS: Six hundred patients who visited the outpatient clinic because of general or trauma surgical indications were asked to participate in this study. They received an invitation letter containing three validated questionnaires to assess LARS (assessed with the LARS score) and both general [European Organization for the Research and Treatment of Cancer (EORTC) QLQ-C30] and colorectal-specific (EORTC QLQ-CR29) QoL. RESULTS: Five hundred and one respondents could be included for the analyses. The median age at inclusion was 68 years and 47.3% were men. Major LARS was observed in 15% of patients (11.4% in men and 18.9% in women, P = 0.021). Women reported more urgency (P = 0.070) and incontinence for both flatus (P < 0.001) and stool (P = 0.063) compared to men. In univariate analyses, women reported major LARS significantly more often than men (OR 1.82; 95% CI 1.10-3.01). Patients with major LARS scored significantly worse in most QoL domains compared to patients with no/minor LARS. CONCLUSION: This is the first study demonstrating major LARS and the association with QoL in a reference population of patients without colorectal cancer. Our data can assist in the interpretation of LARS in past and future research about abdominal complaints after colorectal cancer surgery.

Functional bowel complaints and quality of life after surgery for colon cancer: prevalence and predictive factors.

AIM: Low anterior resection syndrome (LARS) severely affects the quality of life (QoL) of patients after surgery for rectal cancer. There are very few studies that have investigated LARS-like symptoms and their effect on QoL after colon cancer surgery. The aim of this study was to investigate the prevalence of functional abdominal complaints and related QoL after colon cancer surgery compared with patients with similar complaints after rectal cancer surgery. METHOD: All patients who underwent colorectal cancer resections between January 2008 and December 2015, and who were free of colostomy for at least 1 year, were eligible (n = 2136). Bowel function was assessed by the LARS score, QoL by the EORTC QLQ-C30 and QLQ-CR29 questionnaires. QoL was compared between the LARS score categories and tumour height categories. RESULTS: A total of 1495 patients (70.0%) were included in the analyses, of whom 1145 had a colonic and 350 a rectal tumour. Symptoms of LARS were observed in 55% after rectal cancer resection compared with 21% after colon cancer resection. Female gender (OR 1.88, CI 1.392-2.528) and a previous diverting stoma (OR 1.84, CI 1.14-2.97) were independently associated with a higher prevalence of LARS after colon cancer surgery. Patients with LARS after colon cancer surgery performed significantly worse in most QoL domains. CONCLUSION: The results of this study highlight the presence of LARS-like symptoms after surgery for colonic cancer. Patients suffering from major LARS-like symptoms after colon resection reported the same debilitating effect on their QoL as patients with major LARS after rectal resection. This should be addressed by colorectal cancer specialists in order to adequately inform patients.

Phase I Study of Lentiviral-Transduced Chimeric Antigen Receptor-Modified T Cells Recognizing Mesothelin in Advanced Solid Cancers.

This phase I study investigated the safety and activity of lentiviral-transduced chimeric antigen receptor (CAR)-modified autologous T cells redirected against mesothelin (CART-meso) in patients with malignant pleural mesothelioma, ovarian carcinoma, and pancreatic ductal adenocarcinoma. Fifteen patients with chemotherapy-refractory cancer (n = 5 per indication) were treated with a single CART-meso cell infusion. CART-meso cells were engineered by lentiviral transduction with a construct composed of the anti-mesothelin single-chain variable fragment derived from the mouse monoclonal antibody SS1 fused to intracellular signaling domains of 4-1BB and CD3zeta. Patients received 1-3 × 107 or 1-3 × 108 CART-meso cells/m2 with or without 1.5 g/m2 cyclophosphamide. Lentiviral-transduced CART-meso cells were well tolerated; one dose-limiting toxicity (grade 4, sepsis) occurred at 1-3 × 107/m2 CART-meso without cyclophosphamide. The best overall response was stable disease (11/15 patients). CART-meso cells expanded in the blood and reached peak levels by days 6-14 but persisted transiently. Cyclophosphamide pre-treatment enhanced CART-meso expansion but did not improve persistence beyond 28 days. CART-meso DNA was detected in 7/10 tumor biopsies. Human anti-chimeric antibodies (HACA) were detected in the blood of 8/14 patients. CART-meso cells were well tolerated and expanded in the blood of all patients but showed limited clinical activity. Studies evaluating a fully human anti-mesothelin CAR are ongoing.

Activity of Mesothelin-Specific Chimeric Antigen Receptor T Cells Against Pancreatic Carcinoma Metastases in a Phase 1 Trial.

Pancreatic ductal adenocarcinoma (PDAC) is resistant to T-cell-mediated immunotherapy. We engineered T cells to transiently express a messenger RNA encoding a chimeric antigen receptor (CAR) specific for mesothelin, a protein that is overexpressed by PDAC cells. We performed a phase I study to evaluate the safety and efficacy of adoptive cell therapy with autologous mesothelin-specific CAR T cells (CARTmeso cells) in 6 patients with chemotherapy-refractory metastatic PDAC. Patients were given intravenous CARTmeso cells 3 times weekly for 3 weeks. None of the patients developed cytokine release syndrome or neurologic symptoms and there were no dose-limiting toxicities. Disease stabilized in 2 patients, with progression-free survival times of 3.8 and 5.4 months. We used 18F-2-fluoro-2-deoxy-D-glucose (FDG)-positron emission tomography/computed tomography imaging to monitor the metabolic active volume (MAV) of individual tumor lesions. The total MAV remained stable in 3 patients and decreased by 69.2% in 1 patient with biopsy-proven mesothelin expression; in this patient, all liver lesions had a complete reduction in FDG uptake at 1 month compared with baseline, although there was no effect on the primary PDAC. Transient CAR expression was detected in patients' blood after infusion and led to expansion of new immunoglobulin G proteins. Our results provide evidence for the potential antitumor activity of messenger RNA CARTmeso cells, as well as PDAC resistance to the immune response.

Cellular kinetics of CTL019 in relapsed/refractory B-cell acute lymphoblastic leukemia and chronic lymphocytic leukemia.

Tisagenlecleucel (CTL019) is an investigational immunotherapy that involves reprogramming a patient's own T cells with a transgene encoding a chimeric antigen receptor to identify and eliminate CD19-expressing cells. We previously reported that CTL019 achieved impressive clinical efficacy in patients with relapsed/refractory B-cell acute lymphoblastic leukemia (ALL) and chronic lymphocytic leukemia (CLL), including the expansion and persistence of CTL019 cells, which correlates with response to therapy. Here, we performed formal cellular kinetic analyses of CTL019 in a larger cohort of 103 patients treated with CTL019 in 2 different diseases (ALL and CLL). CTL019 was measured in peripheral blood and bone marrow, using quantitative polymerase chain reaction and flow cytometry. CTL019 levels in peripheral blood typically peaked at 10 to 14 days postinfusion and then declined slowly over time. Patients with complete response (CR)/CR with incomplete count recovery had higher levels of CTL019 in peripheral blood, with greater maximal concentration and area under the curve values compared with nonresponding patients (P < .0001 for each). CTL019 transgene levels were measurable up to 780 days in peripheral blood. CTL019 trafficking and persistence were observed in bone marrow and cerebrospinal fluid. CTL019 expansion correlated with severity of cytokine release syndrome (CRS) and preinfusion tumor burden in pediatric ALL. The results described here are the first detailed formal presentation of cellular kinetics across 2 diseases and highlight the importance of the application of in vivo cellular kinetic analyses to characterize clinical efficacy and CRS severity associated with CTL019 therapy.

European Society of Coloproctology Core Outcome Set for haemorrhoidal disease: an international Delphi study among healthcare professionals.

AIM: There is considerable heterogeneity in outcomes in studies reporting on the treatment of haemorrhoidal disease (HD). The aim of this study was to develop a Core Outcome Set (COS) for HD in cooperation with the European Society of Coloproctology. METHOD: A Delphi study was performed according to the Outcome Measures in Rheumatology (OMERACT) methodology. In total 38 healthcare professionals and 30 patients were invited to the panel. Previously, 10 outcome domains and 59 outcomes were identified through a systematic literature review. In this study, these domains and outcomes were formed into one questionnaire for healthcare professionals and a separate questionnaire for patients. Sequential questionnaire rounds prioritizing the domains and outcomes were conducted. Panel members were asked to rate the appropriateness of each domain and outcome on a nine-point Likert scale. During a face-to-face meeting, healthcare professionals agreed on the primary and secondary end-points of the COS for HD. Finally, a short survey was sent to the healthcare professionals in order to reach consensus on how the chosen end-points should be assessed and at which time points. RESULTS: The response rate in questionnaire round 1 for healthcare professionals was 44.7% (n = 17). Sixteen out of 17 healthcare professionals also completed the questionnaire in round 2. The response rate for the patient questionnaire was 60% (n = 18). Seventeen healthcare professionals participated in the face-to-face meeting. The questionnaire rounds did not result in a clear-cut selection of primary and secondary end-points. Most domains and outcomes were considered important, and only three outcomes were excluded. During the face-to-face meeting, agreement was reached to select the domain 'symptoms' as primary end-point, and 'complications', 'recurrence' and 'patient satisfaction' as secondary end-points in the COS for HD. Furthermore, consensus was reached that the domain 'symptoms' should be a patient reported outcome measure and should include the outcomes 'pain' and 'prolapse', 'itching', 'soiling' and 'blood loss'. The domain 'complications' should include the outcomes 'incontinence', 'abscess', 'urinary retention', 'anal stenosis' and 'fistula'. Consensus was reached to use 'reappearance of initial symptoms' as reported by the patient to define recurrence. During an additional short survey, consensus was reached that 'incontinence' should be assessed by the Wexner Fecal Incontinence Score, 'abscess' by physical examination, 'urinary retention' by ultrasonography, 'anal stenosis' by physical examination, and 'fistula' by physical examination and MR imaging if inconclusive. During follow-up, the outcome 'symptoms' should be assessed at baseline, 7 days, 6 weeks and 1 year post-procedure. The outcomes 'abscess' and 'urinary retention' should be assessed 7 days post-procedure and 'incontinence', 'anal stenosis' and 'fistula' 1 year post-procedure. CONCLUSIONS: We developed the first European Society of Coloproctology COS for HD based on an international Delphi study among healthcare professionals. The next step is to incorporate the patients' perspective in the COS. Use of this COS may improve the quality and uniformity of future research and enhance the analysis of evidence.