NCT05253651 · Seagen, a wholly owned subsidiary of Pfizer
A Study of Tucatinib With Trastuzumab and mFOLFOX6 Versus Standard of Care Treatment in First-line HER2+ Metastatic Colorectal Cancer
(MOUNTAINEER-03)
What this study is about
This study is being done to find out if tucatinib with other cancer drugs works better than the usual treatment to treat participants with HER2 positive colorectal cancer. This study will also determine what side effects happen when participants take this combination of drugs. A side effect is anything a drug does to the body besides treating your disease.
View original scientific description
This study is being done to find out if tucatinib with other cancer drugs works better than standard of care to treat participants with HER2 positive colorectal cancer. This study will also determine what side effects happen when participants take this combination of drugs. A side effect is anything a drug does to the body besides treating your disease.
Interventions
DRUG
tucatinib
300mg given by mouth (orally) twice daily
DRUG
trastuzumab
8mg/kg loading dose will be given into the vein (IV; intravenously) on Cycle 1 day 1, followed by 6mg/kg given by IV every 3 weeks thereafter.
DRUG
bevacizumab
5mg/kg given by IV every 2 weeks
DRUG
cetuximab
400mg/m2 loading dose will be given by IV on Cycle 1 day 1, followed by 250mg/m2 given by IV weekly
DRUG
oxaliplatin
85mg/m2 given by IV every 2 weeks. Component of mFOLFOX6.
DRUG
leucovorin
400mg/ m2 given by IV every 2 weeks. Component of mFOLFOX6.
DRUG
levoleucovorin
200mg/ m2 given by IV every 2 weeks. May be given in place of leucovorin. Component of mFOLFOX6.
DRUG
fluorouracil
400mg/m2 given by IV bolus then 2400mg/m2 given by continuous IV infusion (over 46-48 hours) every 2 weeks. Component of mFOLFOX6.
Primary outcome measures
Progression-free survival (PFS) per Response Evaluation Criteria in Solid Tumors Version 1.1 (RECIST v1.1) by Blinded Independent Central Review (BICR)
Time frame: Up to approximately 3 years
The time from the date of randomization to the BICR assessment of disease progression according to RECIST v1.1 or death from any cause
Who can participate
This study lists these criteria on ClinicalTrials.gov. A study coordinator reviews eligibility during screening — this page does not determine whether you qualify.
Inclusion criteria
- Histologically and/or cytologically confirmed adenocarcinoma of the colon or rectum which is locally advanced unresectable or metastatic
- Able to provide the most recently available formalin-fixed paraffin-embedded (FFPE) tumor tissue blocks (or freshly sectioned slides) obtained prior to treatment initiation to a central laboratory
- If archival tissue is not available, a newly-obtained baseline biopsy of an accessible tumor lesion is required within 35 days prior to start of study treatment
- HER2+ disease as determined by a tissue based assay performed at a central laboratory.
- Participant has rat sarcoma viral oncogene homolog wild-type (RAS WT) disease as determined by local or central testing. For central RAS analysis, tissue sample must be analyzed within 1 year of biopsy date.
- Radiographically measurable disease per RECIST v1.1 with:
- At least one site of disease that is measurable and that has not been previously irradiated, or
- If the part
Where
- Glendale, Arizona
- Phoenix, Arizona
- Scottsdale, Arizona
- Anaheim, California
- Baldwin Park, California
- Bellflower, California
- Fontana, California
- Fountain Valley, California
- Glendale, California
- Harbor City, California
- Irvine, California
- Los Angeles, California
And 71 more locations — see the full list below.
Related conditions & keywords
Frequently asked questions
What is a clinical trial?
A clinical trial is a research study that tests new medical treatments, drugs, devices, or procedures to determine their safety and effectiveness. Trials are carefully designed and monitored to protect participants while advancing medical knowledge.
Is it safe to participate?
Clinical trials follow strict safety guidelines and ethical standards. Trials must be reviewed and approved, and participants are closely monitored by medical professionals throughout the study. You can withdraw at any time if you choose.
Will I be compensated?
Many clinical trials offer compensation for your time, travel expenses, and inconvenience. The specific compensation varies by study and will be discussed during the screening process. All study-related medical care is typically provided at no cost to participants.
Will I receive a placebo instead of treatment?
When effective treatment exists, participants typically receive either the standard treatment plus the study intervention, or the standard treatment plus placebo. You would not be denied effective care. Placebos are primarily used when no proven treatment is available, or in addition to standard care. Your trial consent form will clearly explain what treatments you may receive.
Can I leave a trial if I change my mind?
Absolutely. Participation in clinical trials is completely voluntary. You have the right to withdraw from the study at any time, for any reason, without penalty or loss of benefits to which you are otherwise entitled.
How long does a clinical trial last?
Trial duration varies widely depending on the study design and purpose. Some trials last just a few weeks, while others may continue for months or years. The study coordinator will provide specific timeline information during your screening call.
Data: ClinicalTrials.gov · synced Jun 4, 2026 · Source of record for eligibility and locations