FDA OKs Pfizer’s TUKYSA for Front‑line Maintenance in HER2‑Positive Metastatic Breast Cancer

Pfizer said Wednesday that the U.S. Food and Drug Administration approved TUKYSA, or tucatinib, in combination with trastuzumab and pertuzumab as a front-line maintenance treatment for adults with unresectable locally advanced or metastatic HER2-positive breast cancer after induction therapy.

The label expansion matters because it moves TUKYSA from later-line use into an earlier phase of treatment. In practice, first-line care for HER2-positive metastatic breast cancer has long centered on HER2-targeted therapy plus a taxane chemotherapy, followed by maintenance treatment with trastuzumab and pertuzumab. The new approval adds an oral HER2-targeted drug to that maintenance setting after patients complete initial treatment without their disease worsening.

Pfizer said the approval was based on the Phase 3 HER2CLIMB-05 trial, a randomized, double-blind, placebo-controlled study. Patients who completed induction therapy with trastuzumab, pertuzumab and a taxane without progression were randomly assigned to receive tucatinib plus trastuzumab and pertuzumab, or placebo plus trastuzumab and pertuzumab.

The trial enrolled 326 patients in the tucatinib arm and 328 in the placebo arm. Median progression-free survival — the length of time patients lived without their disease getting worse — was 24.9 months with tucatinib, compared with 16.3 months with placebo, an absolute gain of 8.6 months. The hazard ratio for progression or death was 0.641, with a 95% confidence interval of 0.514 to 0.799. The key secondary endpoint of overall survival was not mature at the primary analysis, meaning the study was not yet ready to show whether patients lived longer overall.

Safety remains a central issue with the new use. Pfizer’s materials for the approved regimen include a boxed warning for severe hepatotoxicity, or liver toxicity. In HER2CLIMB-05, the company said 18% of patients had ALT elevations greater than five times the upper limit of normal, while 10% had AST elevations above that threshold. Pfizer also reported five confirmed Hy’s Law cases, a marker of serious drug-related liver injury, including one fatality, all after rechallenge. Other adverse events highlighted by the company included diarrhea, hepatic events and nausea. Liver-function monitoring and dose changes may be required.

TUKYSA was first approved in the United States in 2020 in combination with trastuzumab and capecitabine for previously treated HER2-positive metastatic breast cancer. Pfizer also noted a 2023 accelerated approval for tucatinib plus trastuzumab in HER2-positive metastatic colorectal cancer. The HER2-positive breast cancer treatment landscape has become more competitive since the FDA approved Enhertu plus pertuzumab in late 2025, though this new decision places TUKYSA specifically in the maintenance setting after induction therapy.

At the time of reporting, however, the FDA had not posted a separate public announcement or an updated Drugs@FDA approval summary for the label change. FDA oncology pages note that the agency does not issue a public announcement for every oncology approval or label update, so the approval is being attributed to Pfizer’s announcement.

“These results demonstrate that adding tucatinib to first-line maintenance therapy extends the time patients live without their disease progressing, while maintaining a manageable safety profile, suggesting a promising new potential approach that could advance the current standard of care for HER2-positive disease,” Erika Hamilton, principal investigator for HER2CLIMB-05, said in a Pfizer release last year.