# MOUNTAINEER

Source: https://onco.cc/trials/mountaineer/  
OnCo record `mountaineer` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

A HER2 pill plus antibody gave durable responses in the 3-5% of bowel cancers driven by HER2, and is now being tested as first-line treatment.

## Summary

MOUNTAINEER phase 2: confirmed ORR 38.1%, median duration of response 12.4 months; FDA accelerated approval January 2023 (first HER2-directed regimen in CRC). The randomised phase 3 successor is a separate record, MOUNTAINEER-03 (NCT05253651, 400 patients, primary completion December 2027).

## Fields

- Kind: Trial
- Status: completed
- Last checked: 2026-09-07
- Registry id: NCT03043313
- Phase: 2
- Setting: Chemotherapy-refractory, HER2-positive, RAS wild-type unresectable or metastatic colorectal cancer: tucatinib plus trastuzumab (cohorts A and B) or tucatinib alone (cohort C)
- Sponsor: Pfizer (Seagen)
- Result: Phase 2 ORR 38.1%, DOR 12.4 months; phase 3 ongoing.
- Outcomes: Objective response rate (phase 2): Tucatinib + trastuzumab 38.1 percent

## Notes

- The randomised phase 3 successor is a separate record, `mountaineer-03` (NCT05253651), which is recruiting with primary completion due 31 December 2027.

## Sources

- ClinicalTrials.gov NCT03043313: https://clinicaltrials.gov/study/NCT03043313
- MOUNTAINEER-03 NCT05253651: https://clinicaltrials.gov/study/NCT05253651
- MOUNTAINEER: tucatinib plus trastuzumab for chemotherapy-refractory HER2-positive RAS wild-type metastatic colorectal cancer (Lancet Oncology 2023): https://doi.org/10.1016/S1470-2045(23)00150-X

## Connected records

- cancers: [Colorectal cancer](https://onco.cc/cancers/colorectal/), [HER2-amplified colorectal cancer](https://onco.cc/cancers/her2-amplified-colorectal/)
- technologies: [HER2 tyrosine kinase inhibitors](https://onco.cc/technologies/her2-tyrosine-kinase-inhibitors/), [Small-molecule kinase inhibitors](https://onco.cc/technologies/kinase-inhibitors/)
- targets: [HER2](https://onco.cc/targets/her2/)
- drugs: [Bevacizumab](https://onco.cc/drugs/bevacizumab/), [Cetuximab](https://onco.cc/drugs/cetuximab/), [FOLFOX (5-FU, leucovorin, oxaliplatin)](https://onco.cc/drugs/folfox/), [Oxaliplatin](https://onco.cc/drugs/oxaliplatin/), [Trastuzumab](https://onco.cc/drugs/trastuzumab/), [Tucatinib](https://onco.cc/drugs/tucatinib/)
- companies: [Pfizer (incl. Seagen)](https://onco.cc/companies/pfizer/)
- trials: [DESTINY-CRC01](https://onco.cc/trials/destiny-crc01/), [MOUNTAINEER-03](https://onco.cc/trials/mountaineer-03/), [TRIUMPH](https://onco.cc/trials/triumph/)
- people: [Tanios Bekaii-Saab](https://onco.cc/people/tanios-bekaii-saab/)
- key papers: [Assessment of a HER2 scoring system for colorectal cancer: results from a validation study](https://onco.cc/key-papers/paper-valtorta-her2-scoring-colorectal-heracles-mod-pathol-2015/), [HER2 overexpression and amplification as a potential therapeutic target in colorectal cancer: analysis of 3256 patients enrolled in the QUASAR, FOCUS and PICCOLO colorectal cancer trials](https://onco.cc/key-papers/paper-richman-her2-amplification-quasar-focus-piccolo-j-pathol-2016/), [Tucatinib plus trastuzumab for chemotherapy-refractory, HER2 +, RAS wild-type metastatic colorectal cancer (MOUNTAINEER): final analysis](https://onco.cc/key-papers/paper-mountaineer-nat-commun-2026-update/), [Tucatinib plus trastuzumab for chemotherapy-refractory, HER2-positive, RAS wild-type unresectable or metastatic colorectal cancer (MOUNTAINEER)](https://onco.cc/key-papers/paper-strickler-mountaineer-tucatinib-trastuzumab-lancet-oncol-2023/)
- roadmaps: [Colorectal cancer roadmap: from the adenoma-carcinoma sequence and the first screening trials to total mesorectal excision, oxaliplatin, RAS testing, immunotherapy for mismatch repair-deficient disease, ctDNA-guided treatment and organ preservation](https://onco.cc/roadmaps/colorectal-roadmap/)
- biomarkers: [RAS wild-type (extended KRAS and NRAS testing)](https://onco.cc/biomarkers/ras-wild-type/)

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