Maintenance Treatment in HER2-Positive Metastatic Breast Cancer: HER2CLIMB-05
In this article
A new chapter in maintenance treatment for HER2-positive metastatic breast cancer: What does HER2CLIMB-05 tell us?
HER2-positive metastatic breast cancer accounts for approximately 15–20%of all cases and is an aggressive subtype characterized by HER2 overexpression. Although standard first-line treatments are effective, the risk of disease progression is high, and managing brain metastases is a particularly critical need.
Presented at SABCS 2025, the Phase 3 HER2CLIMB-05 trialevaluated outcomes after induction treatment (taxane + trastuzumab + pertuzumab) in individuals whose disease was controlled, when the oral tyrosine kinase inhibitor tucatinib was added to the maintenance phase. The data show that this strategy significantly delays disease progression.
Note: This content is not medical advice. Treatment decisions should be made by an oncology specialist, considering the patient’s general condition, metastatic sites and adverse-effect profile.
HR 0.64 (p<0.001)
Strong secondary evidence
Intracranial protection
Increased response rate
‘Where’ and ‘as what’ was this study announced?
Primary results were presented at SABCS 2025 in General Session 1 (GS1-01). Study: HER2CLIMB-05 (NCT05132582).
The Scientific Rationale: Dual Blockade + TKI
The antibodies used in standard maintenance (trastuzumab + pertuzumab) are large molecules and may have difficulty crossing the blood–brain barrier. Tucatinib is a small-molecule tyrosine kinase inhibitor with a demonstrated ability to cross the blood–brain barrier. By adding tucatinib to maintenance treatment, this study aimed both to improve systemic control and to protect the brain.
The Key Outcome: Progression-Free Survival (PFS)
What does this difference mean in practice?
Extending median PFS by 8.6 months (a 36% risk reduction) means that, in metastatic disease, patients spend almost an additional year without chemotherapy (using biological agents alone). This is a highly meaningful clinical gain.
Other Efficacy Parameters
Trial design
Phase 3, randomized, double-blind. Patients with HER2+ metastatic disease who received 4–8 cycles of first-line induction (taxane + trastuzumab + pertuzumab) without progression. A total of n=901 patients.
Patients were randomized 1:1 to Tucatinib + HP or Placebo + HP arms.
Safety: A Tolerable Profile
Adverse effects in the tucatinib arm were as expected and generally manageable. The most common events were gastrointestinal effects and changes in hepatic (liver) enzymes.
• Diarrhea (Grade 3+): 20% – Managed with antidiarrheals.
• Elevated ALT/AST: 12% – Generally transient and reversible.
Treatment discontinuation rate
Discontinuation due to adverse eventsHigh adherence
The similarity between the discontinuation rate in the active-drug arm (10%) and the placebo arm (8%) is the strongest indication of how well patients tolerate the treatment.
Practical message
HER2CLIMB-05 suggests that, in maintenance treatment after first-line induction, adding tucatinib may become standard. Particularly in patients at risk of brain metastases, this strategy both controls systemic disease for longer and protects the brain.
Sources: Freedman RA, Tolaney SM, et al. ‘HER2CLIMB-05: randomized study of tucatinib vs placebo…’ J Clin Oncol. 2025;43(suppl 17):LBA1. • Murthy RK, et al. Original HER2CLIMB Study. N Engl J Med. 2020.
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