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Study of Dostarlimab Combined with Short Course Radiotherapy for Locally Advanced Rectal Cancer Patients with Microsatellite Instability

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This study focuses on patients with locally advanced rectal cancer that has specific genetic characteristics - microsatellite unstable or mismatch repair-deficient. These terms refer to specific changes in the cancer cells that affect how DNA repairs itself. The study evaluates a treatment approach combining dostarlimab (marketed as JEMPERLI), which is given through intravenous infusion, with a short course of radiotherapy.

The main purpose of this research is to determine how effective this combination treatment is in controlling the cancer without the need for surgery. The treatment involves receiving dostarlimab infusions along with radiation therapy. After treatment, patients will be monitored to see if their cancer completely disappears, which would allow them to avoid surgery.

During the study, patients will receive dostarlimab infusions at a dose of 500 mg for up to 6 months. The effectiveness of this approach will be evaluated over a two-year period to check if the cancer remains controlled without surgery. Doctors will monitor patients' overall health, how well the cancer responds to treatment, and whether the cancer returns after initial response.

The research process

The trial runs in 4 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Initial treatment phase

    You will receive dostarlimab through an intravenous infusion (medication given directly into a vein)

    The medication used is JEMPERLI 500 mg concentrate mixed into a solution for infusion

    This treatment will be combined with a short course of radiation therapy

  2. Step 2

    Monitoring phase

    Your response to the treatment will be evaluated to check for a complete clinical response (whether the cancer has responded fully to the treatment)

    Regular check-ups will be conducted to monitor your condition

    Your doctor will perform tests to check for any signs of cancer returning

  3. Step 3

    Follow-up assessments

    You will have regular health assessments at 3, 6, 12, and 24 months

    Quality of life questionnaires will be completed at these visits

    Your doctor will monitor for any side effects using standardized criteria

  4. Step 4

    Long-term monitoring

    Your health status will be monitored for up to 36 months

    Regular checks will be performed to ensure the cancer has not returned

    The total duration of the study continues until December 2029

Who can join the trial?

10 criteria

  • Must be at least 18 years old
  • Must have confirmed rectal cancer (adenocarcinoma) with specific genetic characteristics (dMMR/MSI-H) verified through special laboratory tests
  • Cancer must be located in the middle or lower part of the rectum and be in stage II or III
  • Must be able to perform normal daily activities with minimal or no assistance (WHO performance status 0 or 1)
  • Must have adequate liver function as shown by specific blood tests: - Liver enzymes (AST and ALT) within acceptable limits - Normal bilirubin and albumin levels - If cirrhosis present, must be well-controlled (Child-Pugh A)
  • Must have acceptable blood test results: - Adequate hemoglobin (above 9 g/dl) - Sufficient platelet count (above 100 G/L) - Normal white blood cell count - Adequate kidney function
  • Women who can become pregnant must use contraception during treatment and for 4 months after treatment ends
  • Men with partners who can become pregnant must use contraception during treatment and for 4 months after treatment ends
  • Must be able to understand and sign the informed consent form
  • Must have social security coverage

Who cannot join the trial?

12 criteria

  • Age below 18 years old
  • Previous treatments for rectal cancer including surgery, radiation therapy, or chemotherapy
  • Presence of distant metastases (cancer that has spread to other parts of the body)
  • Known allergies or hypersensitivity to study medications
  • Pregnant or breastfeeding women
  • Active or untreated infections
  • Significant heart, liver, or kidney problems that could interfere with treatment
  • Participation in other clinical trials within the past 30 days
  • Mental conditions that could affect the ability to provide informed consent
  • History of other cancers within the past 5 years (except for adequately treated non-melanoma skin cancer)
  • Immunodeficiency conditions (weakened immune system) or active autoimmune diseases
  • Inability to undergo required medical procedures or follow study protocol
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Investigated drugs

  • Dostarlimab

    is an immunotherapy medication that helps your immune system fight cancer cells. It works by blocking a protein called PD-1, which allows your body's immune cells to better recognize and attack cancer cells. It is given through an intravenous infusion (through a vein).

  • Radiotherapy

    is a treatment that uses high-energy radiation beams to target and destroy cancer cells. In this trial, it is given as a short course of treatment (also called short course radiotherapy) to treat rectal cancer. The radiation is precisely directed at the tumor area to minimize damage to surrounding healthy tissue.

What is already known about the treatment

Dostarlimab - A monoclonal antibody medication administered through intravenous infusion that works by blocking PD-1 (programmed cell death protein 1) receptors on immune cells, helping the body's immune system to detect and fight cancer cells. This immunotherapy drug is currently being investigated in clinical trials for treating locally advanced rectal cancer with specific genetic characteristics (microsatellite unstable or mismatch repair-deficient), particularly in combination with short-course radiotherapy. As a PD-1 inhibitor class medication, Dostarlimab represents a targeted immunotherapy approach that has shown promising results in treating various types of cancers, with its mechanism focusing on enhancing the body's natural immune response against cancer cells.

Investigated diseases

Rectal Cancer with MSI/dMMR - A specific type of cancer that develops in the rectum (the last part of the large intestine) with particular genetic characteristics. This cancer has either microsatellite instability (MSI) or deficient mismatch repair (dMMR), which are features related to how DNA repairs itself in cells. The condition typically begins as small growths called polyps that can develop into cancer over time. As the cancer progresses, it can grow through the layers of the rectal wall. This type of rectal cancer is characterized by specific changes in DNA repair mechanisms, making it genetically distinct from other forms of rectal cancer.
Trial detailsLast updated 2 Oct 2026
Age18+ yearsPhasePhase IITrial ID2024-510772-20-00Estimated enrolment68 patientsSponsorCentre Hospitalier Universitaire De Dijon

sourced from the EU Clinical Trials Register and site verification

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On this site, “treatment” means an investigational medicine being studied in a clinical trial. Its safety and efficacy for the use being studied have not yet been confirmed, some participants may receive a placebo or a comparator medicine, and taking part does not guarantee any health benefit. The decision to take part is made by the doctor at the research site. This site is for information only and does not replace medical advice.

This service is not affiliated with the European Commission, the EMA, or the official CTIS system. Most information comes from publicly available international clinical-trial registries, supplemented by data from academic sites, national regulators and commercial sponsors. On this site, “treatment” and “therapy” mean a medicine being tested in a clinical trial. Its safety and effectiveness in the use being studied are not yet confirmed, some participants may receive a placebo or a comparator, and taking part does not guarantee a health benefit. The doctor at the research site decides who can take part. This site provides information, not medical advice. Certain content and visual elements on this website have been generated or enhanced using artificial intelligence (AI).