FDA Approves Tucatinib Maintenance for HER2+ Metastatic Breast Cancer

The FDA approved tucatinib (Tukysa; Pfizer) in combination with trastuzumab and pertuzumab for the maintenance treatment of adults with unresectable locally advanced or metastatic HER2-positive (HER2+) breast cancer following induction treatment, moving the oral HER2-targeted therapy into the frontline setting.^1,2

The approval is based on the phase 3 HER2CLIMB-05 trial (NCT05132582), which found that adding tucatinib to trastuzumab and pertuzumab maintenance extended median progression-free survival (PFS) by 8.6 months compared with placebo.^2,3

Tucatinib Moves Into Frontline Maintenance for HER2+ Metastatic Breast Cancer

HER2 is overexpressed in up to 15% to 20% of breast cancers and is associated with poor prognosis, with an estimated 5-year survival rate of 41% to 47% depending on hormone receptor status.² Tucatinib, an orally administered HER-targeting tyrosine kinase inhibitor, was first approved by the FDA in April 2020 with trastuzumab and capecitabine for adults with advanced unresectable or metastatic HER2-positive breast cancer, including patients with brain metastases, who had received 1 or more prior anti-HER2-based regimens in the metastatic setting.⁴

“Today’s FDA approval marks the next chapter for [tucatinib], bringing it into the front-line maintenance setting and offering patients a chemotherapy-free option that can help delay disease progression after initial treatment,” Aamir Malik, executive vice president and chief US commercial officer at Pfizer, said in a news release.²

HER2CLIMB-05 Shows 8.6-Month PFS Gain With Tucatinib

HER2CLIMB-05 was a randomized, double-blind, placebo-controlled phase 3 trial. Between March 2022 and July 2024, 654 patients who had completed induction therapy with trastuzumab, pertuzumab, and a taxane with no evidence of progression were randomly assigned to tucatinib 300 mg twice daily (n = 326) or placebo (n = 328), each combined with trastuzumab and pertuzumab.^2,3 The primary end point was investigator-assessed PFS, and overall survival is a key secondary end point.²

Adding tucatinib reduced the risk of disease progression or death by 35.9% (HR, 0.64; 95% CI, 0.51-0.80; P < .0001).² Median PFS was 24.9 months (95% CI, 21.3-not reached) in the tucatinib arm vs 16.3 months (95% CI, 12.6-18.7) in the placebo arm. A PFS benefit was observed regardless of brain metastases or hormone receptor status, according to the primary analysis published in the Journal of Clinical Oncology.³

Safety Findings in HER2CLIMB-05

The label carries a boxed warning for severe hepatotoxicity, which was more severe in the trial than in the drug’s previously known safety profile.² The most common adverse reactions (≥20%) with tucatinib were diarrhea, musculoskeletal pain, hepatotoxicity, nausea, fatigue, rash, and vomiting.

Serious adverse reactions occurred in 17% of patients who received tucatinib, including hepatotoxicity in 3.9%, and 1 patient experienced a fatal adverse reaction of drug-induced liver injury. There were 5 confirmed Hy’s Law cases, all following rechallenge with tucatinib, and hepatotoxicity led to discontinuation in 8% of patients.

Diarrhea occurred in 73% of patients who received tucatinib, including grade 3 events in 6%.² The prescribing information recommends monitoring alanine aminotransferase, aspartate aminotransferase, and bilirubin before starting tucatinib, every 2 weeks for the first 2 months, and then every 3 weeks during treatment.

Study Limitations and Investigator Perspective

Survival data in the HER2CLIMB-05 trial remain immature, and the primary PFS analysis was based on investigator assessment.³

“The HER2CLIMB-05 findings support [tucatinib] plus trastuzumab and pertuzumab as a chemotherapy-free maintenance strategy that allows us to target HER2-positive tumors from multiple angles and can help prolong disease control,” Erika Hamilton, MD, principal investigator of HER2CLIMB-05 and director of breast cancer research at Sarah Cannon Research Institute, said in a statement.²

References

FDA approves tucatinib with trastuzumab and pertuzumab for maintenance treatment of HER2-positive breast cancer. FDA. October 7, 2026. Accessed October 7, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-tucatinib-trastuzumab-and-pertuzumab-maintenance-treatment-her2-positive-breast-cancer

Pfizer’s Tukysa regimen receives FDA approval as front-line maintenance treatment for HER2+ metastatic breast cancer. News release. Pfizer. October 7, 2026. Accessed October 7, 2026. https://www.pfizer.com/news/press-release/press-release-detail/pfizers-tukysa-regimen-receives-fda-approval-front-line

Diéras V, Curigliano G, Martin M, et al; HER2CLIMB-05 Investigators. HER2CLIMB-05: a phase III study of tucatinib versus placebo in combination with trastuzumab and pertuzumab as first-line maintenance therapy for HER2+ metastatic breast cancer. J Clin Oncol. 2026;44(17):1597-1607. doi:10.1200/JCO-25-02600

FDA approves tucatinib for patients with HER2-positive metastatic breast cancer. FDA. April 17, 2020. Accessed October 7, 2026. https://www.fda.gov/drugs/resources-information-approved-drugs/fda-approves-tucatinib-patients-her2-positive-metastatic-breast-cancer