# Tucatinib plus trastuzumab for chemotherapy-refractory, HER2 +, RAS wild-type metastatic colorectal cancer (MOUNTAINEER): final analysis

Source: https://onco.cc/key-papers/paper-mountaineer-nat-commun-2026-update/  
OnCo record `paper-mountaineer-nat-commun-2026-update` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Later report from the MOUNTAINEER trial registered as NCT03043313, in Nature Communications (2026); its title describes an updated or longer-term analysis.

## Summary

MOUNTAINEER was a multicenter, open-label, phase 2 trial (NCT03043313) that evaluated the efficacy and safety of tucatinib plus trastuzumab, a dual HER2-targeted chemotherapy-free regimen. Patients were included if they had chemotherapy-refractory, HER2+, RAS wild-type unresectable or metastatic colorectal cancer. This final analysis reports updated efficacy and safety after a median follow-up of 32.4 months. Of the 84 patients who received tucatinib plus trastuzumab, the confirmed objective response rate was 39.3%; median duration of response was 15.2 months. Median progression-free survival was 8.1 months and overall survival was 23.9 months. Efficacy was relatively similar across central HER2+ testing methods. No clear association of treatment response with co-occurring biomarker alterations was seen. Few patients discontinued treatment due to adverse events; no treatment-emergent deaths occurred. Tucatinib plus trastuzumab showed clinically meaningful efficacy and favorable safety. Efficacy was observed irrespective of central HER2+ testing methods and in patients with heterogeneous tumor biomarker profiles.

Indexed on Europe PMC as PubMed record 41526345 (DOI 10.1038/s41467-025-67824-z). Its abstract cites the registry id NCT03043313, which is how it was matched to this trial; no figure has been checked by an editor.

## Fields

- Kind: Key paper
- Last checked: 2026-09-22
- Tags: europepmc-ingest
- Journal: Nature Communications
- Year: 2026
- DOI: 10.1038/s41467-025-67824-z
- Authors: Strickler JH, Cercek A, Siena S, et al.
- What it means: A second publication from the MOUNTAINEER trial, later than the first and described in its title as an update or longer-term analysis. Read it with the primary publication linked from the trial page; the record was linked automatically and its figures have not been checked by hand.
- Caveats: Matched to the trial by the registry id cited in the Europe PMC record; the summary reproduces the record's abstract and no figure has been verified against the full paper.; Chosen as a later report by words in its title (updated, long-term, final, overall survival or a year count), not by reading the paper.

## Sources

- Nat Commun 2026: https://doi.org/10.1038/s41467-025-67824-z
- PubMed: https://pubmed.ncbi.nlm.nih.gov/41526345/
- Europe PMC: https://europepmc.org/article/MED/41526345
- ClinicalTrials.gov NCT03043313: https://clinicaltrials.gov/study/NCT03043313

## Connected records

- trials: [MOUNTAINEER & MOUNTAINEER-03](https://onco.cc/trials/mountaineer/)
- journals: [Nature Communications](https://onco.cc/journals/nature-communications/)

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