# MOUNTAINEER: tucatinib plus trastuzumab for HER2-positive, RAS wild-type metastatic colorectal cancer

Source: https://onco.cc/key-papers/paper-mountaineer-lancet-oncol-2023/  
OnCo record `paper-mountaineer-lancet-oncol-2023` (Key paper). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

The chemotherapy-free combination of tucatinib and trastuzumab shrank tumours in almost four in ten patients with previously treated HER2-positive colorectal cancer, with responses lasting about a year, and became the first approved HER2 regimen for the disease.

## Summary

Phase 2 study of 117 patients with HER2-positive, RAS wild-type unresectable or metastatic colorectal cancer previously treated with chemotherapy, of whom 84 received tucatinib plus trastuzumab.

Objective response was 38.1 percent with a median duration of response of 12.4 months, median progression-free survival 8.2 months and median overall survival 24.1 months; tucatinib alone was less active and patients crossed over to the combination.

## Fields

- Kind: Key paper
- Last checked: 2026-09-17
- Journal: The Lancet Oncology
- Year: 2023
- DOI: 10.1016/S1470-2045(23)00150-X
- Authors: Strickler JH, Cercek A, Siena S, et al.
- Findings: Objective response 38.1 percent; median duration of response 12.4 months.; Median overall survival 24.1 months.
- What it means: HER2 amplification testing is now standard in RAS wild-type metastatic colorectal cancer, and tucatinib-trastuzumab is the approved chemotherapy-free option after first-line therapy.
- Caveats: Single-arm study in a RAS wild-type population; activity in RAS-mutant tumours is not expected.; Confirmatory first-line trial (MOUNTAINEER-03) ongoing.

## Sources

- Lancet Oncol 2023: https://doi.org/10.1016/S1470-2045(23)00150-X
- PubMed: https://pubmed.ncbi.nlm.nih.gov/37142372/

## Connected records

- cancers: [HER2-amplified colorectal cancer](https://onco.cc/cancers/her2-amplified-colorectal/)
- drugs: [Trastuzumab](https://onco.cc/drugs/trastuzumab/), [Tucatinib](https://onco.cc/drugs/tucatinib/)
- trials: [MOUNTAINEER & MOUNTAINEER-03](https://onco.cc/trials/mountaineer/)
- journals: [The Lancet Oncology](https://onco.cc/journals/lancet-oncology/)

---
JSON: https://onco.cc/api/v1/entities/paper-mountaineer-lancet-oncol-2023.json