Pfizer has released compelling new data from its Phase 3 HER2CLIMB-05 clinical trial, showing that the company’s tyrosine kinase inhibitor, TUKYSA® (tucatinib), significantly improved outcomes for patients with HER2-positive metastatic breast cancer (MBC) when used as part of an investigational first-line maintenance therapy. The findings, now published in the Journal of Clinical Oncology and presented at the 48th San Antonio Breast Cancer Symposium (SABCS), highlight the potential for a new therapeutic approach aimed at delaying disease progression without the need for chemotherapy.
The HER2CLIMB-05 trial evaluated TUKYSA in combination with trastuzumab and pertuzumab following chemotherapy-based induction in patients diagnosed with HER2+ metastatic breast cancer. According to Pfizer, the regimen achieved a 35.9% reduction in the risk of disease progression or death compared with the control group receiving placebo plus trastuzumab and pertuzumab. The improvement, measured by investigators, translated into a hazard ratio of 0.641 (95% CI: 0.514-0.799; p<0.0001), demonstrating a statistically significant and clinically meaningful benefit.
One of the most notable findings was the substantial improvement in median progression-free survival (PFS). Patients treated with TUKYSA achieved a median PFS of 24.9 months, compared with 16.3 months in the placebo arm — an extension of 8.6 months. The benefit was consistent across all key patient subgroups, including those with hormone receptor–positive and hormone receptor–negative disease, individuals with de novo or recurrent disease, and patients with or without a history of brain metastases at baseline.
Although the secondary endpoint of overall survival (OS) has not yet reached maturity — only 20% of required events have occurred — early analyses indicate a positive numerical trend in favor of the TUKYSA combination. Further follow-up will be required to determine the full OS impact.
Dr. Erika Hamilton, principal investigator of the trial and Director of Breast Cancer Research at Sarah Cannon Research Institute, emphasized the real-world relevance of the findings. “Most patients with HER2-positive metastatic breast cancer face disease progression within two years of starting first-line treatment,” she said. “These results show that adding tucatinib can significantly extend the time patients live without progression, while maintaining a manageable safety profile.”
Safety data from HER2CLIMB-05 revealed no unexpected concerns. The combination’s side-effect profile aligned with known safety data for each drug, though a higher incidence of asymptomatic Grade ≥3 liver transaminase elevations was noted in the TUKYSA group. These events were generally reversible and managed through dose adjustments. Common adverse events included diarrhea, hepatic effects, and nausea.
Jeff Legos, Pfizer’s Chief Oncology Officer, underscored the broader significance of the trial results. “TUKYSA has become a trusted standard of care for later-line HER2-positive metastatic breast cancer,” he said. “These new findings support its potential role as part of a chemotherapy-free, first-line maintenance strategy. We remain committed to bringing forward treatment options that make a meaningful difference for patients and their families.”
TUKYSA is currently approved in more than 50 countries, including the United States, where it is authorized for use in combination with trastuzumab and capecitabine for adult patients with unresectable or metastatic HER2+ breast cancer who have received one or more prior anti-HER2 therapies. However, it is not yet approved for first-line treatment. Pfizer confirmed that discussions with regulatory authorities are planned following the positive HER2CLIMB-05 findings.
As the company advances conversations with global regulators, the new data could mark a pivotal step toward expanding treatment options for patients with HER2-positive metastatic breast cancer and potentially reshaping the first-line maintenance landscape for this aggressive disease.