Understanding and Tailored Treatment of Low Anterior Resection Syndrome (PATO-LARS)

The goal of this observational study is to learn why some patients develop low anterior resection syndrome (LARS) after colorectal cancer treatment. The study also aims to identify different subtypes of LARS and understand which patients may respond to specific treatments.

The main questions it aims to answer are:

• What physiological and imaging changes are associated with LARS?
• How do patients with LARS differ from patients without LARS after colorectal cancer surgery?
• Are there measurable differences between LARS, patients treated with organ-preserving chemoradiotherapy, and patients with fecal incontinence?

Participants will:

• Complete advanced physiological and imaging assessments related to bowel function

• Be compared with four control groups:

  • patients without LARS after colorectal cancer surgery
  • patients treated with organ-preserving chemoradiotherapy
  • patients with fecal incontinence and urge fecal incontinence
• Take part in a single study visit where all measurements are performed

Study Overview

• Status: Recruiting
• Conditions: Low Anterior Resection Syndrome; Faecal Incontinence; Faecal Incontinence With Faecal Urgency; Colorectal (Colon or Rectal) Cancer Survivors

Detailed Description

Low anterior resection syndrome (LARS) is a common long-term complication after colorectal cancer surgery. Up to 80% of patients experience symptoms such as urgency, frequent bowel movements, clustering, and fecal incontinence. These symptoms can severely affect quality of life, and the underlying causes are not fully understood. LARS appears to result from several interacting mechanisms, including sensory changes, altered motility, reduced reservoir function, sphincter dysfunction, and effects of chemotherapy or radiotherapy. Because different patients may have different dominant mechanisms, treatment responses vary widely.

This observational study aims to investigate the physiological and imaging characteristics of LARS using advanced assessment methods. The goal is to better understand the mechanisms behind LARS, identify distinct patient subtypes, and support development of more targeted treatment strategies.

The study will include 50 patients with minor or major LARS after rectal cancer surgery. Their results will be compared with four control groups:

• patients who had rectal cancer surgery but did not develop LARS,
• patients with fecal incontinence (before/after sacral nerve stimulation),
• patients with urge fecal incontinence (before/after dorsal genital nerve stimulation), and
• patients treated with organ-preserving chemoradiotherapy ("watch-and-wait"), whose rectum has not been surgically removed.

All participants will attend a single study visit that includes advanced physiological measurements, Magnetic Resonance Imaging (MRI)-based assessments, and standardized questionnaires. These methods are not part of routine clinical care but are used to explore mechanisms such as motility, sensory function, sphincter activity, and rectal reservoir function.

Patients with LARS will also be followed during their standard stepwise treatment pathway. They will complete questionnaires before and during each treatment step, which may include dietary advice, medication, pelvic floor training (biofeedback), and rectal emptying techniques such as mini-enemas or transanal irrigation. This follow-up will help determine how different physiological patterns relate to treatment response.

The study is conducted in collaboration between Aarhus University Hospital and Aalborg University Hospital, with expert input from The Royal London Hospital (UK) and Motilis SA (Switzerland).

• Study Type: Observational
• Enrollment (Estimated): 145

Contacts and Locations

• Study Contact: Name: Esben B Mark, PhD; Phone Number: +45 97663523; Email: e.mark@rn.dk

Study Locations

• Denmark
  • Aalborg, Denmark, 9220
    • Active, not recruiting
    • Aalborg University Hospital
  • Aarhus, Denmark, 8200
    • Recruiting
    • Aarhus University Hospital
    • Contact: Gitte K Sørensen, Research Nurse; Phone Number: +45 2499 5223; Email: gittesoe@rm.dk
    • Principal Investigator: Peter Christensen, MD, Professor
  • Vejle, Denmark, 7100
    • Recruiting
    • Vejle Hospital
    • Contact: Bettina H Ingemann, Research Nurse; Phone Number: +45 7940 9831; Email: Bettina.Hugger.Ingemann@rsyd.dk

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult; Older Adult
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

During outpatient visits, the treatment responsible doctor will identify eligible patients. Patients will be recruited at the following departments:

1. LARS patients - patient operated for rectal cancer at Department of Surgery, Aarhus University Hospital, with rectal resection with sphincter preservation and primary anastomosis.
2. Watch and wait patients - patient treated for rectal cancer with organ preservation at Aalborg University Hospital or Vejle Hospital.
3. Patients with Faecal Incontinence planned for neuromodulation at Pelvic Floor Unit, Department of Surgery, AUH.

Description

Inclusion Criteria:

General:

• Must be able to read and understand Danish.
• All participants must be adults and >18 years and have full legal capacity.
• Assessed by study personnel to have understood the research protocol, being able to comply with investigation procedures as well as ability to come to the hospital at the agreed timepoints, and to complete the trial.

Specific inclusion criteria for LARS patients:

• Patients operated for rectal cancer with a rectal resection and sphincter preserving surgery at a minimum of three months postop.
• If patients have received a temporary protective ileostomy, this should have been reversed for a minimum of three months postop.

Specific inclusion criteria for fecal incontinence patients and urge fecal incontinence patients

• Patients planned for neuromodulation.
• Satisfactory interoperative test results leading to permanent implantation of a pacemaker for sacral nerve modulation.

Specific inclusion criteria for "watch and wait" patients:

• Rectum/colon cancer patients treated with organ-preserving treatment, i.e., chemotherapy and radiotherapy with a complete clinical and radiological response at a minimum of 12 months posttreatment.

Exclusion Criteria:

General exclusion criteria

• Persons that are not able to understand information
• Connective tissue disorders
• Parkinson's disease
• Non-MRI compatible pacemaker, clips or other metal objects in the body. Patients implanted with a pacemaker for sacral nerve modulation will not undergo MRI postoperatively.
• Piercings that cannot be removed before MRI
• Claustrophobia
• Allergic to latex
• Abdominal diameter equal or more than 140 cm
• Have other individual factors, in the opinion of the physician/healthcare professional, in which participating is contraindicated
• Participation in concomitant clinical trial
• Known intestinal obstruction, significant intestinal strictures or perforation. If in doubt about intestinal stricture, the patient will be examined with MRI of the small intestine, colonoscopy or other supplementing examination
• Disorders of swallowing
• Pregnant women

Specific exclusion criterias for LARS patients

• History of anastomotic leakage following rectal resection and sphincter preserving therapy
• Evidens of local recurrence or dessimination of the cancer

Study Plan

How is the study designed?

Number of groups / cohorts

5

Cohorts and Interventions

Group / Cohort
LARS, minor or major symptoms; LARS score ≥ 20; Patients operated for rectal cancer with a rectal resection and sphincter preserving surgery at a minimum of three months postoperative. If patients have received a temporary protective ileostomy, this should have been reversed for a minimum of three months postoperative.
LARS, no symptoms; LARS score < 20; Patients operated for rectal cancer with a rectal resection and sphincter preserving surgery at a minimum of three months postoperative. If patients have received a temporary protective ileostomy, this should have been reversed for a minimum of three months postoperative.
Faecal Incontinence; Patients planned for neuromodulation; Satisfactory interoperative test results leading to permanent implantation of a pacemaker for sacral nerve modulation
Faecal Incontinence, urge; Patients planned for neuromodulation; Satisfactory interoperative test results leading to permanent implantation of a pacemaker for sacral nerve modulation; Faecal urgency occurring ≥3 episodes per week, with or without associated Faecal incontinence (≥1 episode per week), and a St. Mark's Incontinence Score of ≥9
Watch and wait; Rectum/colon cancer patients treated with organ-preserving treatment, i.e., chemotherapy and radiotherapy with a complete clinical and radiological response at a minimum of 12 months posttreatment

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
EuroQol 5-Dimension, 5-Level quality-of-life questionnaire	The EuroQol 5-Dimension, 5-Level questionnaire assesses generic health-related quality of life across five domains: mobility, self-care, usual activities, pain/discomfort, and anxiety/depression. Each domain has five response levels ranging from "no problems" to "extreme problems." Score range and direction: Higher scores indicate better health-related quality of life. Includes a visual analogue scale (0-100) where higher scores indicate better self-rated health.	From baseline visit to the end of each standardized treatments at 4 weeks
Low Anterior Resection Syndrome Score	The Low Anterior Resection Syndrome (LARS) Score is a disease-specific symptom questionnaire assessing bowel dysfunction after low anterior resection. It includes five items covering incontinence, frequency, clustering, urgency, and impact on daily life. Score range and direction: Total score ranges from 0 to 42. Higher scores indicate more severe bowel dysfunction. Severity categories: 0-20: No LARS 21-29: Minor LARS 30-42: Major LARS	From baseline visit to the end of each standardized treatments at 4 weeks

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
St Mark's Incontinence score	Description: The St. Mark's Incontinence Score assesses the severity of fecal incontinence across multiple domains, including incontinence to gas, liquid, and solid stool, urgency, use of pads, and lifestyle impact. Score range and direction: Total score ranges from 0 to 24. Higher scores indicate more severe fecal incontinence.	• Applied at baseline and four weeks into all treatment periods
Colostomy Impact Score	The Colostomy Impact Score is a disease-specific questionnaire evaluating the impact of living with a colostomy on daily functioning, social participation, body image, and emotional well-being. Score range and direction: Total score ranges from 0 to 100. Higher scores indicate greater negative impact of the colostomy on quality of life.	From baseline visit to the end of each standardized treatments at 4 weeks
Bristol Stool Form Scale	The Bristol Stool Form Scale classifies stool consistency into seven categories ranging from hard, lumpy stools to entirely liquid stools. It is used as an indicator of bowel transit and stool form. Score range and direction: Scale ranges from Type 1 to Type 7. Lower types (1-2) indicate harder stools and slower transit. Middle types (3-4) indicate normal stool form. Higher types (6-7) indicate loose or watery stools and faster transit.	From baseline visit to the end of each standardized treatments at 4 weeks
Patient Assessment of Constipation Symptoms (PAC-SYM)	The Patient Assessment of Constipation Symptoms questionnaire measures symptom severity in constipation across three domains: abdominal symptoms, stool symptoms, and rectal symptoms. Score range and direction: Each item is scored 0-4; total score ranges from 0 to 48. Higher scores indicate more severe constipation symptoms.	From baseline visit to the end of each standardized treatments at 4 weeks
Wexner Incontinence Score	The Wexner Incontinence Score evaluates the severity of fecal incontinence based on frequency of incontinence to gas, liquid, and solid stool, need for pads, and lifestyle alteration. Score range and direction: Total score ranges from 0 to 20. Higher scores indicate more severe fecal incontinence.	From baseline visit to the end of each standardized treatments at 4 weeks
Hospital Anxiety and Depression Scale (HADS)	The Hospital Anxiety and Depression Scale assesses symptoms of anxiety and depression in medical populations. It consists of two subscales: HADS-Anxiety and HADS-Depression. Score range and direction: Each subscale ranges from 0 to 21. Higher scores indicate more severe symptoms of anxiety or depression. Total score (0-42) may be reported but is less commonly used.	From baseline visit to the end of each standardized treatments at 4 weeks
Whole gut and segmental transit times as measured with 3D-Transit	Whole-gut and segmental gastrointestinal transit times are measured using the Motilis 3D-Transit system. The system tracks the movement of an electromagnetic capsule through the gastrointestinal tract, allowing calculation of segmental transit times (stomach, small intestine, colon) and total whole-gut transit time. This measure evaluates gastrointestinal motility patterns at baseline. Score range and direction: Transit times are continuous measures reported in minutes or hours. There is no fixed upper or lower limit, as transit times vary physiologically between individuals. Longer transit times indicate slower gastrointestinal motility. Shorter transit times indicate faster gastrointestinal motility.	At baseline
Colonic and segmental colonic volumes	Magnetic resonance imaging is used at baseline to quantify total colonic volume and segmental colonic volumes (ascending, transverse, descending, sigmoid/rectum colon). Volumes are derived from semi-automated segmentation of the colon on T2-weighted images. This measure evaluates baseline colonic morphology and storage capacity. Score range and direction: Colonic volumes are continuous measures reported in milliliters (mL). There is no fixed upper or lower limit, as volumes vary physiologically between individuals. Higher values indicate larger colonic or segmental volume. Lower values indicate smaller colonic or segmental volume.	At baseline
Resting Anal Pressure Measured by High-Resolution Anorectal Manometry	Resting anal pressure will be measured using high-resolution anorectal manometry according to standard manometric protocols. Resting anal pressure reflects basal anal sphincter tone, primarily related to internal anal sphincter function. The outcome will be reported as a continuous physiological measure in millimeters of mercury (mmHg). There are no fixed minimum or maximum values because pressures vary physiologically between individuals. Higher values indicate higher resting anal sphincter tone, while lower values indicate reduced resting sphincter tone.	At baseline
Maximal Voluntary Anal Squeeze Pressure Measured by High-Resolution Anorectal Manometry	Maximal voluntary anal squeeze pressure will be measured using high-resolution anorectal manometry according to standard manometric protocols. Squeeze pressure reflects voluntary external anal sphincter contractile strength. The outcome will be reported as a continuous physiological measure in millimeters of mercury (mmHg). There are no fixed minimum or maximum values because pressures vary physiologically between individuals. Higher values indicate stronger voluntary anal sphincter contraction, while lower values indicate reduced voluntary sphincter contractile function.	At baseline
Rear-Front Pressure Gradient Measured by the Fecobionics Device	The rear-front pressure gradient will be measured using the Fecobionics device during simulated stool evacuation. The Fecobionics device records axial pressure patterns during defecation. The rear-front pressure gradient reflects the pressure difference between the rear and front sensors of the device during evacuation and provides a measure of propulsive force relative to outlet resistance. The outcome will be reported as a continuous physiological measure in millimeters of mercury (mmHg). There are no fixed minimum or maximum values because values vary physiologically between individuals. Higher values indicate stronger propulsive pressure relative to outlet resistance, whereas lower values may indicate impaired propulsion or increased outlet resistance.	At baseline
Compare the physiological findings in LARS patients with controls	Compare the physioligal findings in LARS patients with a) no-LARS patients, b) organ-preservation patients and c) patient with fecal incontinence	At baseline
Investigate the physiological changes in anorectal function associated with neuromodulation in patients with urge fecal incontinence	Changes in anorectal function measured by the Fecobionics Device	From baseline to after 30 minutes of active neuromodulation
Investigate the physiological changes in anorectal function associated with neuromodulation in patients with urge fecal incontinence	Changes in anorectal function measured by high-resolution anorectal manometry	From baseline to after 30 minutes of active neuromodulation
Investigate the physiological changes in anorectal function associated with neuromodulation in patients with fecal incontinence	Changes in anorectal function measured by the Fecobionics Device	From baseline to after active neuromodulation at Visit 2
Investigate the physiological changes in anorectal function associated with neuromodulation in patients with fecal incontinence	Changes in anorectal function measured by high-resolution anorectal manometry	From baseline to after active neuromodulation at Visit 2
Change in VAS Urgency Score From Before to During Stimulation at the Baseline Visit	The participant's perceived urgency to defecate during the examination will be assessed using a visual analogue scale. Participants with fecal incontinence will rate their urgency to defecate on a numeric scale from 0 to 10, where 0 indicates no desire to defecate and 10 indicates maximal urgency. The outcome will be reported as the change in VAS urgency score from the pre-stimulation assessment to the stimulation assessment at the baseline visit. Higher scores indicate stronger urgency to defecate.	Baseline visit: immediately before stimulation and during active stimulation
Resting-State Electroencephalography	Resting-state electroencephalography is recorded with the participant at rest to assess baseline cortical activity patterns. Measures include spectral power across standard frequency bands (theta, alpha, beta). Score range and direction: Spectral power values are continuous and do not have fixed upper limits. Higher or lower values reflect differences in cortical activity depending on frequency band.	At baseline
Evoked Potential Amplitude During Rectal Balloon Distension	Electroencephalography is recorded during rapid rectal balloon distension to elicit cortical evoked potentials. The primary measure is the amplitude of the evoked response to visceral stimulation. Score range and direction: Amplitude is measured in microvolts (µV). Higher amplitudes indicate stronger cortical responses to visceral stimulation.	At baseline
Evoked Potential Latency During Rectal Balloon Distension	Electroencephalography is recorded during rectal balloon distension to measure the latency of cortical evoked potentials, reflecting the timing of sensory pathway activation. Score range and direction: Latency is measured in milliseconds (ms). Longer latencies indicate slower or delayed cortical processing. Shorter latencies indicate faster neural conduction.	At baseline
Defecation Index Measured by the Fecobionics Device	The defecation index will be derived from Fecobionics measurements obtained during simulated stool evacuation. The index summarizes expulsion performance and anorectal function based on prespecified Fecobionics-derived variables. The outcome will be reported as a continuous index value. There are no fixed minimum or maximum values. Higher values indicate more efficient expulsion and better defecatory performance, whereas lower values indicate reduced defecatory performance.	Baseline

Collaborators and Investigators

• Sponsor: Aalborg University Hospital
• Collaborators: Aarhus University Hospital; Danish Cancer Society; Vejle Hospital
• Investigators: Principal Investigator: Peter Christensen, MD, Professor, Pelvic Floor Unit, Department of Surgery, Aarhus University Hospital

Study record dates

Study Major Dates

• Study Start (Actual): September 17, 2024
• Primary Completion (Estimated): December 31, 2026
• Study Completion (Estimated): December 31, 2026

Study Registration Dates

• First Submitted: April 20, 2026
• First Submitted That Met QC Criteria: May 1, 2026
• First Posted (Actual): May 7, 2026

Study Record Updates

• Last Update Posted (Actual): May 7, 2026
• Last Update Submitted That Met QC Criteria: May 1, 2026
• Last Verified: May 1, 2026

More Information

Terms related to this study

• Keywords: LARS
• Additional Relevant MeSH Terms: Mental Disorders; Postoperative Complications; Pathologic Processes; Signs and Symptoms, Digestive; Intestinal Diseases; Behavioral Symptoms; Elimination Disorders; Digestive System Diseases; Gastrointestinal Diseases; Rectal Diseases; Colonic Diseases; Pathological Conditions, Signs and Symptoms; Behavior; Signs and Symptoms; Low Anterior Resection Syndrome; Encopresis
• Other Study ID Numbers: R325-A19027

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO
• IPD Plan Description: Individual participant data will not be shared because the study involves sensitive health information and data protection regulations (GDPR) prevent public sharing of identifiable or de-identified participant-level data.

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No