Research on Effective Strategies After Immunotherapy for Mismatch Repair-deficient Early-stage GI Tumors (RESIST)

September 14, 2026 updated by: University Hospital, Basel, Switzerland

This cohort study is divided into two parts:

Part A: Registry Cohort All patients with non-metastatic, MMRd/MSI-H colorectal cancers (and other gastrointestinal cancers for exploratory analysis) who have signed the general research consent will be included in a prospective registry. This includes patients who undergo primary surgical resection (+/- neoadjuvant/adjuvant therapy) or following immunotherapy, regardless of response.

Part A is a multicenter observational registry with both prospective and retrospective enrolment. Prospective enrolment includes eligible patients entered into the registry after activation of the study at the respective participating site. Retrospective enrolment includes eligible patients diagnosed on or after 1 January 2024 whose clinical data were generated prior to registry activation. Both prospectively and retrospectively enrolled patients contribute to the registry analyses.

Part B: Active Surveillance Cohort (Surveillance Study) A subset of patients from Part A who achieve a complete or near-complete response to ICI therapy, wish to avoid surgery, and are deemed appropriate for non-operative management by a multidisciplinary tumor board are offered inclusion in a phase II surveillance study (Part B). Patients enrolled in Part B will be analysed for the primary endpoint.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Detailed Description

Background and Rationale: Mismatch repair-deficient (MMRd) or microsatellite instability-high (MSI-H) gastrointestinal (GI) cancers represent a distinct molecular subtype characterized by high tumor mutational burden and increased immunogenicity. Immune checkpoint inhibitors (ICIs) have demonstrated remarkable efficacy in this population, with recent studies showing high rates of pathological complete response (pCR) when used in the neoadjuvant setting for non-metastatic GI cancers and colorectal cancers in particular. These results raise important questions about the necessity of surgical resection in patients who achieve complete clinical response (cCR) after ICI therapy.

Avoiding surgery in patients with complete response through an active surveillance approach could significantly reduce treatment-related morbidity and improve quality of life for selected patients. However, this strategy remains investigational and robust clinical evidence is lacking regarding its safety, long-term oncologic outcomes and appropriate selection criteria. Our study seeks to address this gap by evaluating response-guided, non-operative management in patients with non-metastatic MMRd/ MSI-H GI tumors treated primarily with immunotherapy.

Objectives: The primary objective of this study is to evaluate 2-year relapse-free survival (RFS) in patients with non-metastatic, mismatch repair-deficient (MMRd) or microsatellite instability-high (MSI-H) in patients with stage II/III colorectal cancer who achieve a complete or near-complete response following primary treatment with immune checkpoint inhibitors (ICIs) who enter Part B of the study (surveillance study).

Method: Eligible patients may receive immune checkpoint inhibitor (ICI) therapy as the primary treatment for mismatch repair-deficient (MMRd) or microsatellite instability-high (MSI-H), locally advanced, non-metastatic gastrointestinal cancer according to local practice. Treatment regimens include PD-(L)1 monotherapy (e.g., pembrolizumab, atezolizumab) or combination ICI therapy (e.g., nivolumab plus ipilimumab), administered at the discretion of the treating oncologist for up to 6 months (in case of near complete response ICI may be continued up to a total of 12 months following multidisciplinary evaluation).

Patients who do not achieve a complete or near-complete clinical response-or who are not eligible or not willing to undergo non-operative management-proceed to standard oncological surgery (with or without neo-/adjuvant systemic therapy), in accordance with clinical guidelines. Postoperatively, they receive routine oncological follow-up per institutional standards and remain in registry cohort (Part A).

Patients who demonstrate a complete or near-complete clinical response to ICI and are considered eligible for non-surgical management (based on multidisciplinary evaluation), enter an intensified surveillance program in lieu of immediate surgery (Part B).

The active surveillance includes Clinical assessments, Cross-sectional imaging (e.g., CT or MRI) , Endoscopic evaluations at defined intervals and Facultative ctDNA testing 6 months after completion of immunotherapy (Part B)

Study Type

Observational

Enrollment (Estimated)

234

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • Switzerland
      • Basel, Switzerland, 4031
        • Recruiting
        • Universitätsspital Basel
        • Contact:
      • Biel, Switzerland, 2501
        • Recruiting
        • Spitalzentrum Biel
        • Contact:
      • Lucerne, Switzerland, 6000
        • Recruiting
        • Luzerner Kantonsspital
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Sampling Method

Non-Probability Sample

Study Population

The study population includes adult patients with non-metastatic MSI-H/MMRd gastrointestinal cancers, specifically colorectal (colon and rectal) cancer as well as gastro-oesophageal and gastric adenocarcinoma. Eligible participants must have achieved a complete or near-complete clinical response following immune checkpoint inhibitor therapy, with no radiologic, endoscopic, or histologic evidence of residual disease at the time of response assessment. Patients are enrolled into a structured active surveillance program instead of undergoing immediate surgical resection. Individuals with metastatic disease, insufficient response to immunotherapy or contraindications to surveillance procedures are excluded.

Description

Inclusion Criteria:

Part A and Part B:

  • Consent and Capacity:
  • Participant is 18 years of age or older.
  • Participant is legally competent and able to provide informed consent.
  • Participant has provided the appropriate written consent
  • Diagnosis: Histologically confirmed gastro-oesophageal, colon or rectum cancer, showing mismatch repair-deficiency (MMRd) by immunohistochemistry (loss of immunoreactivity for at least one of the following proteins: MLH1, PMS2, MSH2 and/or MSH6).
  • Clinical Stage: Non-metastatic, locally advanced disease, defined as:
  • cT2-T4, cN0-2, cM0 for gastro-oesophageal or rectum cancer
  • cT4 and/or cN+, cM0 for colon cancer
  • Therapy with immune checkpoint inhibitor (ICI) as primary treatment, either:
  • Combination ICI therapy (e.g., anti-PD-1 plus anti-CTLA-4 such as nivolumab + ipilimumab) or
  • Single-agent ICI therapy (e.g., pembrolizumab, atezolizumab, or other anti- PD(L)1 agents)

Part B only:

  • Patient consents to participate in surveillance study
  • Complete or near complete response (*) to primary ICI treatment, as determined by local multidisciplinary team (MDT) assessment, based on restaging 8 weeks after termination of the ICI treatment:
  • Radiological imaging (CT/MRI/PET-CT),
  • Endoscopic findings, and

  • Clinical parameters (e.g., normalization of tumor markers, absence of symptoms **)

    • Note: in case of near complete response up to a total of 12 months of ICI is allowed following multidisciplinary team (MDT) discussion. After diagnosis of a near-complete response, tumor reassessments should be performed every 3 months up to a total treatment period of 12 months. If a complete tumor response is observed within the 12-month period, it should be recorded as the best overall response.

      • Note: Assessment of complete or near complete response does not incorporate ctDNA test results

Exclusion Criteria:

  • Recurrent Disease: Known history of previously treated gastrointestinal cancer with recurrence at time of inclusion.
  • Metastatic Disease: Evidence of distant metastases (M1) at any point prior to or during ICI therapy.
  • Other Malignancies: Active second malignancy (excluding non-melanoma skiN cancer or in-situ cervical carcinoma) that may interfere with study outcomes or surveillance.

Part B only:

  • Inadequate response to ICI: Patients with progressive disease, stable disease, or partial response deemed unsuitable for non-operative management.
  • Prior Treatment: Any prior systemic therapy, radiotherapy or surgery for the current colon cancer diagnosis before ICI treatment (except biopsy)
  • Medical or Psychiatric Conditions: Significant comorbid conditions or psychiatric illness that, in the opinion of the investigator, would impair the patient's ability to comply with protocol requirements, including surveillance.
  • Logistical Barriers: Social, geographic, or organizational factors (e.g., lack of access to regular follow-up care, inability to attend surveillance visits) that would prevent adherence to the active surveillance protocol.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Intervention / Treatment
Active Surveillance after ICI response instead of surgery
Participants with mismatch repair-deficient (MMRd) or microsatellite instability-high (MSI-H) stage II/III gastrointestinal cancer who achieve a complete or near-complete response after immune checkpoint inhibitor (ICI) therapy enter a structured active surveillance program instead of undergoing immediate surgery. Surveillance includes scheduled radiologic imaging, endoscopic evaluation, clinical assessment, and biomarker monitoring to detect relapse early and allow timely salvage treatment.
Other: Active surveillance after complete response to immunotherapy in MMRd GI cancers

Eligible patients may receive immune checkpoint inhibitor (ICI) therapy as the primary treatment for mismatch repair-deficient (MMRd) or microsatellite instability-high (MSI-H), locally advanced, non-metastatic gastrointestinal cancer according to local practice. In case of near complete response ICI may be continued up to a total of 12 months following multidisciplinary evaluation.

Part A includes all patients with stage II or III colorectal cancer (esophageal adenocarcinoma, gastric cancer will be allowed as well) confirmed as MMRd/MSI-H. Patients are enrolled regardless of treatment strategy, including those receiving immune checkpoint inhibitor (ICI) therapy or primary surgery.

A subset of patients from Part A who achieve a complete or near-complete response to ICI therapy, wish to avoid surgery, and are deemed appropriate for non-operative management by a multidisciplinary tumor board are offered inclusion in a phase II active surveillance protocol (Part B).

Other Names:
  • watch and wait
Standard of Care Cohort
Patients that receive an operation to remove the primary tumour after completion of immunecheckpoint therapy for MSI high colorectal cancer (resp. other MSI high GI cancer).
Other: Stand of Care
Patients in the Standard of care Arm (Arm A) will receive a resection of the primary tumour after completion of the immunecheckpoint inhibition therapy.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Relapse-Free Survival (RFS)
Time Frame: 24 months
The proportion of patients with colorectal cancers who remain free from local, regional, or distant recurrence at 24 months after achieving a complete or near-complete clinical response to immune checkpoint inhibitor therapy and undergoing active surveillance. Recurrence is defined as radiologic, endoscopic, or histologic evidence of tumor regrowth requiring salvage surgery or systemic treatment.
24 months

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Relapse-Free Survival - other GI Cancers
Time Frame: 24 months
applied to patients with non-metastatic MMRd/MSI-H gastroesophageal or other GI cancers entering active surveillance.
24 months
Clinical Complete Response (cCR) Rate
Time Frame: 12 months
Proportion of patients achieving clinical complete response, near-complete response, partial response, stable disease, or progressive disease following ICI therapy, assessed by radiologic, endoscopic, clinical criteria, and biopsy results.
12 months

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

University Hospital, Basel, Switzerland

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

September 1, 2026

Primary Completion (Estimated)

August 31, 2033

Study Completion (Estimated)

August 31, 2033

Study Registration Dates

First Submitted

September 14, 2026

First Submitted That Met QC Criteria

September 14, 2026

First Posted (Actual)

September 18, 2026

Study Record Updates

Last Update Posted (Actual)

September 18, 2026

Last Update Submitted That Met QC Criteria

September 14, 2026

Last Verified

September 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • RESIST

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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