Contribute to HER2-positive metastatic colorectal cancer treatment research
The MOUNTAINEER-03 Study is testing the effects of a new treatment combination that may impact how certain cancers are managed.


About the MOUNTAINEER-03 Study
The MOUNTAINEER-03 clinical research study is evaluating how well a study drug combination works compared to standard therapy for RAS-WT, HER2-positive colorectal cancer that is metastatic and/or unresectable. Metastatic means the cancer has spread to other parts of the body, such as the lung or brain.1 Unresectable means the cancer cannot be removed by surgery.
In order to participate, a person cannot have received treatment for metastatic colon cancer. It’s okay if someone has had treatment for earlier stage colon cancer.
This clinical research study will aim to find out how the investigational study drug combination works compared to the current standard of care for those living with RAS-WT, HER2-positive metastatic colorectal cancer. This study will also test which side effects happen when participants take this combination of drugs.
Why Is This Study Being Done?
This study is being done to test how tucatinib, trastuzumab, and mFOLFOX6 work to treat cancer of the colon or rectum that is RAS-WT and HER2-positive. This combination of drugs is investigational, and it is being compared to the standard treatment with mFOLFOX6 alone or with either bevacizumab or cetuximab.
Tucatinib
Tucatinib is a drug that is designed to target and turn off HER2. People who are HER2-positive have cells that make more HER2 than normal, which can lead to cancer. Turning off HER2 in cancer cells may make the cancer cells die or slow down their growth.
In this study, tucatinib is used with trastuzumab. Trastuzumab is an antibody that is designed to attach to HER2. Antibodies are part of the immune system and usually help protect from getting sick. By attaching to HER2, trastuzumab may slow down or stop tumor cell growth.
Who Can Take Part?
Participants may be able to take part in the clinical research study if they:
- Are aged 18 and older
- Have cancer of the colon or rectum that has spread to other parts of the body or is hard to remove with surgery
- Have cancer that is RAS-WT and HER2-positive
Please note that this is not a complete list of eligibility criteria. There will be additional health-related questions and some medical tests to confirm eligibility for the clinical research study.

Why Participate?
People who qualify and decide to participate in the clinical research study will help advance medical knowledge about RAS-WT, HER2-positive metastatic colorectal cancer.
Clinical Research Study Participation and Safety
While the clinical research study is ongoing, a team of study doctors and nurses at the study site will closely monitor participants’ health. A study team member is available to answer questions or concerns at any point throughout the clinical research study.
There are also risks involved in the MOUNTAINEER-03 Study, including possible side effects from study treatment. This study drug combination may have little, if any, benefit to participants.
Participation is voluntary, and participants are free to withdraw at any time, for any reason.
Clinical Research Study Locations
Locations shown may have changed in some cases. Please call the number listed in the location results to confirm the nearest study site. Talk with a study site member for more information.
Frequently Asked Questions
About the MOUNTAINEER-03 Study
The MOUNTAINEER-03 Study is being conducted to evaluate how well a study drug combination works when given with the standard therapy compared to standard therapy alone for HER2-positive colorectal cancer that is metastatic and/or unresectable. In order to participate, participants cannot have received treatment for metastatic colon cancer. It’s okay if they have had treatment for earlier stage colon cancer.
Seagen is performing the MOUNTAINEER-03 Study. Seagen is a global biotechnology company that develops and commercializes transformative cancer therapies.
Deciding to participate in a clinical research study is an important and personal decision. Before agreeing to participate, the study team will review all aspects of the clinical research study with potential participants. They will be given a document called an Informed Consent Form that provides, in writing, the clinical research study’s purpose, assessments, procedures, benefits, risks, and precautions. They will have the opportunity to ask questions and are encouraged to speak with their own physician to decide if taking part is right for them.
Some study-related care and investigational study drug costs may be covered. Participants may be reimbursed for expenses relating to attending study appointments such as travel, as per local regulations. The study team can provide more information.
No, all participants will receive either the investigational drug therapy or the standard therapy.
The investigational drug therapy includes:
Investigational study drug (tucatinib)
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Investigational study drug (trastuzumab)
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Standard chemotherapy (mFOLFOX6)
The standard therapy includes:
Standard chemotherapy (mFOLFOX6)
The study doctor will also add one of the following:
bevacizumab
cetuximab
Yes, participation in any clinical research study is completely voluntary. If someone decides to participate, they will be able to choose to stop taking part at any time and for any reason. If they choose to stop taking part, this will not affect their medical care and they will still receive the standard of care treatment. They should talk to their study doctor about leaving the clinical research study so that they can schedule a final evaluation.
About Clinical Research Studies
A clinical research study, also known as a clinical trial, is a scientific study that evaluates the safety and effectiveness of an investigational study drug.
In order to ensure that a clinical research study is ethical, and that patients’ rights are protected, Institutional Review Boards (IRBs) or Ethics Committees (ECs) review study protocols.
An investigational study drug is a medication that has not been approved by regulatory or health authorities (eg, US Food and Drug Administration [FDA], European Medicines Agency [EMA], or appropriate regulatory authorities in each country) for prescription use.