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Petosemtamab versus cetuximab plus drug combination as first‑line treatment for adults with metastatic left‑sided colorectal cancer

Verified siteFast replyRegistered drugNo placebo
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What is this trial about?

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

The study involves people with Colorectal Cancer, a cancer that starts in the colon or rectum. It focuses on tumors that are RAS and BRAF Wild-type, left-sided. One group will receive a new medicine called Petosemtamab together with a standard chemotherapy mix known as mFOLFOX6 or FOLFIRI. The chemotherapy mix contains several drugs that are given through a vein, including folinic acid, irinotecan hydrochloride, oxaliplatin, and fluorouracil. The other group will receive the existing medicine cetuximab combined with the same chemotherapy mix.

The purpose of the trial is to find out which treatment works better as the first therapy for this type of cancer. Participants receive the assigned medicines by IV infusion (a slow drip into a vein) every two weeks. During the study doctors perform imaging scans, such as CT scans, to see if the tumor is shrinking, and they continue treatment until the cancer grows again or side effects become too strong.

The study will record how long patients live without the tumor getting worse, any side effects they experience, and changes in daily activities or symptoms, using questionnaires that ask about pain, energy, and overall well‑being.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Randomization and Assignment to Treatment Group

    After joining the study, you will be randomly placed into one of two groups. One group receives petosemtamab together with a chemotherapy regimen, and the other group receives cetuximab together with the same chemotherapy options.

  2. Step 2

    Start of First Treatment Cycle

    On the first day of the cycle, the assigned study drug is given by IV infusion. The dose of petosemtamab is 1500 mg, and the dose of cetuximab is 500 mg per square meter of body‑surface area.

  3. Step 3

    Administration of Chemotherapy Regimen

    If you are assigned to the mFOLFOX6 regimen, you will receive the following medicines on the same day:

    Oxaliplatin 85 mg per square meter, calcium folinate 400 mg per square meter, and fluorouracil 400 mg per square meter, all given by IV infusion.

    If you are assigned to the FOLFIRI regimen, you will receive the following medicines on the same day:

    Irinotecan hydrochloride 180 mg per square meter, calcium folinate 400 mg per square meter, and fluorouracil 400 mg per square meter, all given by IV infusion.

  4. Step 4

    Monitoring During the Cycle

    After the infusions, you will be observed for any immediate side effects. Vital signs and any symptoms will be recorded by the study staff.

  5. Step 5

    Repeat Treatment Cycles

    The same sequence of drug administration is repeated at the start of each subsequent treatment cycle, continuing until the doctor decides to stop treatment because of disease progression, unacceptable side effects, or completion of the planned study period.

  6. Step 6

    End of Treatment and Follow‑up

    When treatment ends, you will continue to have scheduled visits to assess the status of the cancer and any long‑term effects of the therapy.

Who can join the trial?

5 criteria

  • Confirmed left‑side colon cancer that cannot be removed by surgery or has spread to other parts of the body – a doctor has examined tissue under a microscope (histology or cytology) and determined the tumor is on the left side of the colon and is either unresectable (cannot be cut out) or metastatic (has spread).
  • KRAS and NRAS “wild‑type” (normal) results from a next‑generation sequencing (NGS) test done in a certified laboratory – the tumor must not have specific genetic changes in the KRAS or NRAS genes; this is checked with a modern DNA test (NGS) performed in a lab that meets quality standards (such as a CLIA‑certified lab in the U.S. or an accredited lab elsewhere).
  • No previous systemic cancer treatment for this stage of disease – the patient must not have received chemotherapy, targeted therapy, or other medicines that travel through the whole body for unresectable or metastatic colon cancer.
  • Eligibility to receive either the mFOLFOX6 or FOLFIRI chemotherapy regimen – the patient must be able to take one of these standard chemotherapy combinations (mFOLFOX6 includes drugs like oxaliplatin, 5‑fluorouracil, and leucovorin; FOLFIRI includes irinotecan, 5‑fluorouracil, and leucovorin) according to local medical guidelines.
  • Adult patient of any gender – the study includes men and women who are adults.

Who cannot join the trial?

6 criteria

  • Having a known prior or current right‑sided colorectal cancer (cancer located in the right part of the colon).
  • Having any of the following tumor characteristics: a BRAF V600 mutation (a change in the BRAF gene), MSI‑H/dMMR (a type of DNA repair problem), ERBB2/HER2 positive or amplified (extra copies or high activity of the HER2 protein), or an activating HRAS mutation (a change that makes the HRAS gene overly active).
  • Having previously received any medication that targets EGFR (the epidermal growth factor receptor), such as certain antibodies, protein products, or other similar drugs.
  • Having a known complete DPD deficiency or specific DPYD gene variants that cause a total loss of DPD enzyme activity (DPD helps break down some chemotherapy drugs).
  • If you are planned to receive the chemotherapy regimen FOLFIRI, being homozygous for the UGT1A1*28 or *6 alleles or having a combination of these alleles (which can affect how the body processes certain drugs).
  • Having any type of adenocarcinoma that is not from the colon or rectum (a non‑colorectal adenocarcinomatous disease).
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Investigated drugs

  • Petosemtamab

    is an investigational antibody that is designed to help the immune system recognize and attack cancer cells. In this study it is given through an IV infusion and is being tested to see if it works better than an existing treatment when combined with standard chemotherapy.

  • Folinic acid (calcium folinate)

    is a form of vitamin B9 that is used to protect normal cells from the harmful effects of certain chemotherapy drugs. It is given by IV infusion and helps reduce side effects while allowing the chemotherapy to work more effectively.

  • Irinotecan

    is a chemotherapy medicine that interferes with the DNA of cancer cells, stopping them from growing and dividing. It is administered through an IV infusion and is part of the FOLFIRI chemotherapy regimen used in the trial.

  • Oxaliplatin

    is a chemotherapy drug that damages the DNA of cancer cells, which leads to cell death. It is given by IV infusion and is a key component of the mFOLFOX6 chemotherapy regimen tested in the study.

  • Fluorouracil

    is a chemotherapy agent that blocks the production of DNA and RNA in cancer cells, preventing them from multiplying. It is delivered by IV infusion and is included in both the mFOLFOX6 and FOLFIRI chemotherapy combinations.

  • Cetuximab

    is an approved antibody that targets a protein on the surface of cancer cells, helping to stop their growth. In this trial it is used as a comparator, given by IV infusion together with the same chemotherapy regimens to see how it compares with the investigational drug.

What is already known about the treatment

  • Petosemtamab

    It is administered by intravenous infusion as a sterile solution. The drug is still experimental and is being studied in clinical trials for colorectal cancer. It works by binding to a target on cancer cells and helping the immune system recognize and destroy them. Petosemtamab is classified as a monoclonal antibody.

  • Calcium folinate

    It is given by intravenous infusion as a solution for injection. This medication is approved and widely used to protect normal cells during chemotherapy for colorectal cancer. It supplies a form of folate that helps healthy cells repair DNA and reduces side‑effects of other drugs. Calcium folinate is a folate analog vitamin supplement.

  • Irinotecan

    It is delivered through intravenous infusion in a sterile solution. Irinotecan is an approved chemotherapy drug commonly used for colorectal cancer. It blocks an enzyme called topoisomerase I, which cancer cells need to copy their DNA, thereby stopping their growth. Irinotecan belongs to the class of topoisomerase inhibitors.

  • Oxaliplatin

    It is given by intravenous infusion as a concentrated solution. Oxaliplatin is an approved chemotherapy agent for colorectal cancer. It forms links in the DNA of cancer cells, preventing them from dividing and leading to cell death. Oxaliplatin is classified as a platinum‑based chemotherapy drug.

  • Fluorouracil

    It is administered by intravenous infusion as a solution for injection. Fluorouracil is an approved treatment for colorectal cancer. It mimics a natural building block of DNA and interferes with the cancer cell’s ability to make new DNA, slowing tumor growth. Fluorouracil is an antimetabolite chemotherapy agent.

  • Cetuximab

    It is given as an intravenous infusion in a sterile solution. Cetuximab is an approved monoclonal antibody used for colorectal cancer with certain genetic features. It blocks the epidermal growth factor receptor (EGFR) on cancer cells, stopping signals that tell the cells to grow. Cetuximab belongs to the class of EGFR‑targeting monoclonal antibodies.

Investigated diseases

Colorectal Cancer - Colorectal cancer is a malignant growth that begins in the lining of the colon or rectum, often developing from precancerous polyps. Over time the tumor can enlarge and invade through the bowel wall, reaching nearby lymph nodes. It may also spread through the blood or lymphatic system to distant organs such as the liver, lungs, or peritoneum. When the disease extends beyond the original site, it is described as unresectable or metastatic. As it progresses, symptoms such as changes in bowel habits, bleeding, or abdominal discomfort may become more noticeable.
Trial detailsLast updated 21 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2026-525883-17-00Protocol codeGCT1158-08Estimated enrolment759 patientsSponsorGenmab A/S

sourced from the EU Clinical Trials Register and site verification

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