The United States (US) Food and Drug Administration (FDA) approved tucatinib (Tukysa, Seagen Inc., a subsidiary of Pfizer) in combination with trastuzumab and pertuzumab on October 7, 2026, for the maintenance treatment of adults with unresectable locally advanced or metastatic HER2-positive breast cancer (BC) following induction treatment.
The approval was supported by primary progression-free survival (PFS) data from HER2CLIMB-05, a randomized, double-blind, placebo-controlled trial, in which tucatinib plus trastuzumab and pertuzumab reduced the risk for progression or death by 36% compared with placebo plus trastuzumab and pertuzumab. Overall survival (OS) data were immature at the time of the analysis.
Key finding
In HER2CLIMB-05, tucatinib combined with trastuzumab and pertuzumab maintenance extended median progression-free survival to 24.9 months versus 16.3 months with placebo (HR 0.64; p<0.0001), though OS data remain immature.
Study Design
| Trial | HER2CLIMB-05 (NCT05132582); randomized, double-blind, placebo-controlled |
|---|---|
| Population | 654 adults with HER2-positive unresectable locally advanced or metastatic BC (mBC), with or without brain metastases, who had no evidence of disease progression after 4–8 cycles of induction therapy with trastuzumab, pertuzumab, and a taxane |
| Treatment | Tucatinib 300 mg orally twice daily or placebo, each in combination with trastuzumab and pertuzumab (intravenous [IV] or subcutaneous [SC] fixed-dose combination with hyaluronidase); hormone receptor-positive patients could continue endocrine therapy; treatment continued until disease progression or unacceptable toxicity |
| Primary endpoint | PFS by investigator assessment per RECIST v1.1 |
| Key secondary endpoints | OS |
HER2CLIMB-05 enrolled patients regardless of brain metastasis status, an inclusion criterion that reflects the established risk for HER2-positive mBC to spread to the central nervous system. Patients were permitted to receive a SC fixed-dose combination of trastuzumab, pertuzumab, and hyaluronidase as an alternative to IV administration of the individual agents.
Results and Safety
Median PFS was 24.9 months (95% CI: 21.3, not reached) in the tucatinib arm compared with 16.3 months (95% CI: 12.6, 18.7) in the placebo arm, representing a hazard ratio of 0.64 (95% CI: 0.51, 0.80; p<0.0001). The FDA did not disclose objective response rates or other tumor-response metrics in the approval summary.
Overall survival data were not mature at the time of the primary PFS analysis and no interim results were reported.
The prescribing information carries a boxed warning for hepatotoxicity. Additional warnings and precautions include diarrhea, embryo-fetal toxicity, and increases in serum creatinine that do not reflect impairment of renal function. The recommended tucatinib dose is 300 mg orally twice daily, continued until disease progression or unacceptable toxicity.
Clinical Context
The standard first-line maintenance backbone for HER2-positive mBC following taxane-based induction has been dual HER2 blockade with trastuzumab and pertuzumab. This approval introduces a third targeted agent to that maintenance platform, extending the median PFS benefit by more than eight months in the trial population. The inclusion of patients with brain metastases is clinically notable, as this subgroup has historically been underrepresented or excluded from pivotal trials in HER2-positive mBC.
However, it remains unclear whether the PFS improvement with the addition of tucatinib to trastuzumab and pertuzumab will translate into an OS benefit. Furthermore, the relative PFS benefit in the brain metastasis subgroup was not specifically reported in the FDA’s approval announcement, and longer-term tolerability data in the maintenance setting have not yet been published.
Sources
- U.S. Food and Drug Administration. “FDA Approves Tucatinib, Trastuzumab, and Pertuzumab for Maintenance Treatment of HER2-Positive Breast Cancer.” Drug approval announcement. October 7, 2026. View source.
AI disclosure: This article was prepared with assistance from generative AI using the source material cited above. It was reviewed and edited by Jessica Nye, PhD, before publication.
