# Tucatinib
**Tucatinib** (brand name Tukysa) is an oral, small-molecule tyrosine kinase inhibitor that selectively blocks the HER2 receptor tyrosine kinase, used with other HER2-directed drugs to treat HER2-positive breast cancer and HER2-positive metastatic colorectal cancer. It was initially developed by Array BioPharma and subsequently by Seattle Genetics (Seagen Inc., now a subsidiary of Pfizer), and received its first FDA approval in April 2020.[1](https://pubmed.ncbi.nlm.nih.gov/32548668/)
| Key fact | Detail |
|---|---|
| Drug class | Oral, highly selective HER2 tyrosine kinase inhibitor that does not significantly inhibit EGFR[1](https://pubmed.ncbi.nlm.nih.gov/32548668/) • [2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/) |
| First approval | FDA approval on 17 April 2020, with trastuzumab and capecitabine, for advanced unresectable or metastatic HER2-positive breast cancer including brain metastases[3](https://www.tga.gov.au/sites/default/files/auspar-tucatinib-210317.pdf) |
| Pivotal trial | HER2CLIMB (N = 612, randomized 2:1): median PFS 7.8 vs 4.9 months (HR 0.57); median OS 24.7 vs 19.2 months (HR 0.73)[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/) |
| Brain metastases | CNS progression-free survival 9.9 vs 4.2 months in patients with brain metastases[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/) |
| Colorectal indication | FDA accelerated approval in January 2023 with trastuzumab for RAS wild-type HER2-positive metastatic colorectal cancer, based on the MOUNTAINEER trial (ORR 38%)[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/) |
| Dosage | 300 mg orally twice daily, with or without food; 200 mg twice daily in severe hepatic impairment[5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3) |
| Major warnings | Boxed warning for severe and fatal hepatotoxicity; warnings for diarrhea, embryo-fetal toxicity, and increased serum creatinine without affecting renal function[5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3) |
## Mechanism and selectivity
Tucatinib inhibits the tyrosine kinase domain of the HER2 receptor (human epidermal growth factor receptor 2), and in vitro studies in HER2-expressing tumor cells have shown suppression of downstream signaling and inhibition of cell proliferation; in vivo studies showed growth inhibition of HER2-expressing tumors. Combining tucatinib with trastuzumab produced greater antitumor activity in vitro and in vivo than either drug alone.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/) One review also describes dual inhibition of the kinase domains of HER2 and HER3.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/)
Its distinguishing property is selectivity. Tucatinib inhibits the HER2 kinase domain without significant inhibition of other targets such as EGFR, the epidermal growth factor receptor.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/) Broad EGFR inhibition disrupts signaling in normal skin and gastrointestinal lining, which is why older HER2-targeted kinase inhibitors such as lapatinib and neratinib are associated with rashes and diarrhea; tucatinib's selectivity is credited with lower toxicity and with making it easier to combine with monoclonal antibodies and antibody-drug conjugates.[6](https://www.sciencedirect.com/topics/medicine-and-dentistry/tucatinib) In one kinase assay, tucatinib showed a HER2 IC50 of 6.9 nmol/L compared with 109 nmol/L for lapatinib, while neratinib was similar to tucatinib at 5.5 nmol/L.[7](https://www.dovepress.com/treating-advanced-unresectable-or-metastatic-her2-positive-breast-canc-peer-reviewed-fulltext-article-BCTT)
## Development and first approval
The first clinical trial of tucatinib, then known as ONT-380, was a dose-escalation study in patients with metastatic HER2-positive breast cancer, most of whom had received several prior treatments; results published in *Clinical Cancer Research* from the 2013 study showed a more favorable toxicity profile than the dual EGFR/HER2 or pan-HER kinase inhibitors available at the time, with liver enzyme elevations at higher doses that usually improved when the dose was held or reduced.[8](https://www.aacr.org/blog/2025/12/11/tracking-the-history-of-tucatinib-for-breast-cancer-treatment-at-sabcs/) A subsequent trial in patients with progressive, measurable brain metastases tested tucatinib with trastuzumab alone and established 300 mg twice daily as the maximum tolerated dose.[8](https://www.aacr.org/blog/2025/12/11/tracking-the-history-of-tucatinib-for-breast-cancer-treatment-at-sabcs/)
The pivotal HER2CLIMB trial enrolled 612 patients with HER2-positive metastatic breast cancer previously treated with trastuzumab, pertuzumab, and trastuzumab emtansine (T-DM1), including patients with brain metastases, and randomized them 2:1 to tucatinib or placebo added to trastuzumab and capecitabine.[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/) • [9](https://www.nejm.org/doi/full/10.1056/nejmoa1914609) Median progression-free survival was 7.8 months with tucatinib versus 4.9 months with placebo (hazard ratio 0.57), and median overall survival was 24.7 versus 19.2 months (hazard ratio 0.73).[4](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/) Among patients with brain metastases, CNS progression-free survival was 9.9 versus 4.2 months.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/)
On 17 April 2020 the FDA approved tucatinib in combination with trastuzumab and capecitabine for adult patients with advanced unresectable or metastatic HER2-positive breast cancer, including patients with brain metastases, who had received one or more prior anti-HER2-based regimens in the metastatic setting.[3](https://www.tga.gov.au/sites/default/files/auspar-tucatinib-210317.pdf) Tucatinib was the first new molecular entity reviewed under Project Orbis, an international parallel-review pathway of the FDA Oncology Center of Excellence; the FDA, Health Canada, Singapore's Health Sciences Authority, Swissmedic, and Australia's TGA reviewed the application collaboratively, and the drug was also approved in Australia, Canada, Singapore, and Switzerland in 2020.[3](https://www.tga.gov.au/sites/default/files/auspar-tucatinib-210317.pdf) • [8](https://www.aacr.org/blog/2025/12/11/tracking-the-history-of-tucatinib-for-breast-cancer-treatment-at-sabcs/)
## Colorectal cancer and later indications
In the MOUNTAINEER trial, tucatinib was given with trastuzumab to patients with refractory HER2-positive metastatic colorectal cancer, producing an objective response rate of 38% with a favorable safety profile. This led to the FDA's accelerated approval of tucatinib with trastuzumab in January 2023 for adult patients with RAS wild-type, HER2-positive unresectable or metastatic colorectal cancer that had progressed after fluoropyrimidine-, oxaliplatin-, and irinotecan-based chemotherapy; the colorectal indication is approved under accelerated approval based on tumor response rate and durability of response.[2](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/) • [5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3)
**Frontline maintenance.** The FDA sanctioned tucatinib for use alongside trastuzumab and pertuzumab as maintenance therapy in adults with HER2-positive breast cancer that is locally advanced and unresectable or that has metastasized, once induction therapy has been completed, on October 7, 2026. The approval rests on HER2CLIMB-05 (NCT05132582), a randomized, double-blind, placebo-controlled trial in 654 patients who had no evidence of disease progression after induction with trastuzumab, pertuzumab, and a taxane; median progression-free survival was 24.9 months with tucatinib versus 16.3 months with placebo (hazard ratio 0.64), with overall survival data not mature at the time of the analysis.[10](https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-tucatinib-trastuzumab-and-pertuzumab-maintenance-treatment-her2-positive-breast-cancer)
## Safety
Tucatinib carries a boxed warning for hepatotoxicity: it can cause severe and fatal liver injury, particularly after rechallenge, and liver function tests must be obtained before and during treatment, with dose withholding, reduction, or discontinuation based on severity.[5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3) It can also cause severe diarrhea, including dehydration, hypotension, acute kidney injury, and death, and can cause fetal harm.[5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3) The most common adverse reactions (20% or more) with tucatinib, trastuzumab, and capecitabine in metastatic breast cancer are diarrhea, palmar-plantar erythrodysesthesia, nausea, hepatotoxicity, vomiting, stomatitis, decreased appetite, anemia, and rash.[5](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3) In the HER2CLIMB trial, concomitant use with trastuzumab did not produce an increased incidence of adverse cardiac events in the combination arm.[11](https://www.ema.europa.eu/en/documents/assessment-report/tukysa-epar-public-assessment-report_en.pdf)
## Ongoing research
Clinical trials continue across settings, including tucatinib with trastuzumab and mFOLFOX6 in first-line HER2-positive metastatic colorectal cancer, a comparison of RO7771950 against the tucatinib-trastuzumab-capecitabine regimen in breast cancer, and studies of tucatinib with T-DM1 in HER2-positive solid tumors with brain metastases.[12](https://www.cancer.gov/research/participate/clinical-trials/intervention/tucatinib) Open questions noted in the literature include whether tucatinib is effective after progression on lapatinib or neratinib, and no randomized trial has compared tucatinib with neratinib.[7](https://www.dovepress.com/treating-advanced-unresectable-or-metastatic-her2-positive-breast-canc-peer-reviewed-fulltext-article-BCTT) • [13](https://www.mdlinx.com/article/oral-her2-directed-therapy-in-metastatic-breast-cancer-selection-starts-upstream-of-the-tki/6BDfEGBxEr03V683TN5pQl)
## References
1. [Tucatinib: First Approval, Drugs (2020), PubMed](https://pubmed.ncbi.nlm.nih.gov/32548668/)
2. [The History and Development of HER2 Inhibitors, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC10610116/)
3. [Australian Public Assessment Report for Tucatinib (AusPAR), Therapeutic Goods Administration, March 2021](https://www.tga.gov.au/sites/default/files/auspar-tucatinib-210317.pdf)
4. [Twenty-five years with HER2 targeted therapy, PMC](https://pmc.ncbi.nlm.nih.gov/articles/PMC11193558/)
5. [TUKYSA (tucatinib) tablets, Full Prescribing Information, DailyMed](https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=f27eb1b9-b7fc-424e-988f-84dd7bb195a3)
6. [Tucatinib - an overview, ScienceDirect Topics](https://www.sciencedirect.com/topics/medicine-and-dentistry/tucatinib)
7. [Treating advanced unresectable or metastatic HER2-positive breast cancer: a spotlight on tucatinib, Breast Cancer Targets and Therapy, Dove Medical Press](https://www.dovepress.com/treating-advanced-unresectable-or-metastatic-her2-positive-breast-canc-peer-reviewed-fulltext-article-BCTT)
8. [Tracking the History of Tucatinib for Breast Cancer Treatment at SABCS, AACR Cancer Research Catalyst blog](https://www.aacr.org/blog/2025/12/11/tracking-the-history-of-tucatinib-for-breast-cancer-treatment-at-sabcs/)
9. [Tucatinib, Trastuzumab, and Capecitabine for HER2-Positive Metastatic Breast Cancer, New England Journal of Medicine 2020;382:597-609](https://www.nejm.org/doi/full/10.1056/nejmoa1914609)
10. [FDA approves tucatinib with trastuzumab and pertuzumab for the maintenance treatment of HER2-positive breast cancer, FDA](https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-tucatinib-trastuzumab-and-pertuzumab-maintenance-treatment-her2-positive-breast-cancer)
11. [Tukysa, INN-tucatinib, EMA Public Assessment Report](https://www.ema.europa.eu/en/documents/assessment-report/tukysa-epar-public-assessment-report_en.pdf)
12. [Clinical Trials Using Tucatinib, National Cancer Institute](https://www.cancer.gov/research/participate/clinical-trials/intervention/tucatinib)
13. [Oral HER2-directed therapy in metastatic breast cancer, MDLinx](https://www.mdlinx.com/article/oral-her2-directed-therapy-in-metastatic-breast-cancer-selection-starts-upstream-of-the-tki/6BDfEGBxEr03V683TN5pQl)
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*Topic: Encyclopedia › Physical world and mathematics › Chemistry › Organic substances › Pharmaceutical and drug molecules › Tyrosine kinase inhibitors*
*Initially written Oct 21, 2026*
*Copyright 2026 EdgeChat AI, a subsidiary of Biostate AI.*
License: Edgepedia Community License 1.0, https://www.edgepedia.org/edgepedia/license