Pfizer presents data for Tukysa in HER2-positive breast cancer

Pfizer has presented detailed data for its HER2-targeted therapy Tukysa (tucatinib) at the 2025 San Antonio Breast Cancer Symposium, demonstrating significant efficacy in first-line maintenance therapy for HER2-positive breast cancer. The phase III HER2CLIMB-05 trial evaluated adding Tukysa to standard maintenance therapy with Herceptin and Perjeta after induction chemotherapy. The study included 654 patients and showed that adding Tukysa reduced the risk of progression or death by 35.9%, with median progression-free survival (PFS) extended to 24.9 months, 8.6 months longer than control.

Subgroup efficacy

The benefit was consistent across prespecified subgroups, with a greater effect in HR-negative patients (44.6% PFS improvement) versus HR-positive patients (27.5% PFS improvement). This suggests that Tukysa may play a larger role in HR-negative HER2-positive breast cancer populations. At data cutoff, only 7.8% of patients had died, and a trend toward improved overall survival was observed with a numerical 46.1% reduction in risk of death.

Safety profile

Tukysa was generally well tolerated. The most common adverse events were diarrhea, nausea, and elevated liver enzymes, mostly low grade. Grade 3 or higher treatment-emergent adverse events occurred in 42.3% of patients in the Tukysa arm compared with 24.4% in the control arm. One death in each group was attributed to adverse events.

Clinical practice

These results highlight a potential new first-line maintenance strategy for HER2-positive breast cancer, particularly in HR-negative disease, and may influence treatment sequencing alongside other HER2-directed therapies. The data provide clinicians with evidence to consider Tukysa as part of early maintenance regimens and inform decision-making in HER2-positive patient populations.