Tukysa adds a chemotherapy-free maintenance option for HER2-positive metastatic breast cancer; liver toxicity monitoring remains a key consideration.
The FDA has approved Pfizer’s Tukysa (tucatinib) in combination with trastuzumab and pertuzumab as maintenance treatment for adults with unresectable locally advanced or metastatic human epidermal growth factor receptor 2 (HER2)-positive breast cancer who have completed induction therapy, the company announced Oct. 7.1
The decision moves the oral therapy from later-line use into the first-line setting, where it is added to an established antibody pair.
The label expansion extends a product first approved in 2020 into an earlier treatment window.
“Since its first approval in 2020, Tukysa has become an important treatment for patients with second-line HER2+ metastatic breast cancer,” said Aamir Malik, executive vice president and chief U.S. commercial officer of Pfizer.1 “Today's FDA approval marks the next chapter for Tukysa, bringing it into the front-line maintenance setting and offering patients a chemotherapy-free option that can help delay disease progression after initial treatment. This approval reflects Pfizer’s commitment to advancing therapies across the breast cancer treatment journey and delivering meaningful new options for people living with metastatic breast cancer.”
The approval rests on HER2CLIMB-05, a randomized, double-blind, placebo-controlled phase 3 study. Participants had finished induction therapy with trastuzumab, pertuzumab, and a taxane without evidence of progression.
They were then assigned to Tukysa plus trastuzumab and pertuzumab (326 patients) or placebo plus the same two antibodies (328 patients). The primary endpoint was progression-free survival as assessed by the investigator.1
Median progression-free survival reached 24.9 months with Tukysa versus 16.3 months with placebo, a difference of 8.6 months (hazard ratio, 0.64; 95% confidence interval, 0.51-0.80; P<0.0001).1 The results were published in the Journal of Clinical Oncology and presented at the 2025 San Antonio Breast Cancer Symposium.1,2
Pfizer’s release lists overall survival as a key secondary endpoint, and its disclosures note that the trial has yet to establish whether that endpoint will be met.1
HER2 is overexpressed in up to 15% to 20% of breast cancers and is associated with poor prognosis; Pfizer cites an estimated five-year survival of 41% to 47%, depending on hormone receptor status.1
Pertuzumab and trastuzumab with docetaxel has long served as first-line therapy. In a phase 3 trial of that regimen, median overall survival was 57.1 months versus 40.8 months with placebo, trastuzumab, and docetaxel, and the investigators concluded in 2020 that it remained the standard of care.3
“The treatment landscape for HER2+ metastatic breast cancer has evolved dramatically over the past decade, but many patients still experience disease progression despite initial benefit from therapy,” said Erika Hamilton, M.D., principal investigator of HER2CLIMB-05 and chief development officer, late phase, and director of breast cancer research at Sarah Cannon Research Institute.1 “The HER2CLIMB-05 findings support TUKYSA plus trastuzumab and pertuzumab as a chemotherapy-free maintenance strategy that allows us to target HER2-positive tumors from multiple angles and can help prolong disease control.”
Tukysa is an orally administered kinase inhibitor of HER2. The FDA first approved it on April 17, 2020, with trastuzumab and capecitabine for advanced unresectable or metastatic HER2-positive breast cancer, including brain metastases, after one or more prior anti-HER2 regimens.
That approval was based on the 612-patient HER2CLIMB trial.4 Pfizer describes the drug as a National Comprehensive Cancer Network Category 1 option for second-line and later use and reports five approved breast cancer medicines and one biosimilar.1
Pfizer said safety was generally consistent with the known profile of Tukysa, except for increased severity of hepatotoxicity. Most events were asymptomatic and reversible with dose modification or discontinuation.
Adverse events in at least 20% of patients were diarrhea, musculoskeletal pain, hepatotoxicity, nausea, fatigue, rash, and vomiting. Serious hepatotoxicity occurred in 3.9% of patients, including one fatal case of drug-induced liver injury, and hepatotoxicity led to discontinuation in 8%.1
The label carries a boxed warning for severe hepatotoxicity and calls for liver function testing before and during treatment. The prescribing information also describes five confirmed Hy’s Law cases, all following rechallenge.1
Several limits frame the data. The primary analysis relied on investigator assessment, and overall survival results are not yet available. The control arm received dual antibody maintenance, so the 8.6-month difference reflects what Tukysa adds to that backbone rather than a comparison with other strategies.
The term chemotherapy-free applies to the maintenance phase only; trial participants first completed induction chemotherapy. Whether longer progression-free survival translates into a survival benefit, and how clinicians weigh it against hepatotoxicity monitoring, are questions the current data do not answer.
Sources
1. Pfizer’s TUKYSA regimen receives FDA approval as front-line maintenance treatment for HER2+ metastatic breast cancer. News release. Pfizer Inc. October 7, 2026. Accessed October 7, 2026.
2. Hamilton E, et al. HER2CLIMB-05: a phase III study of tucatinib versus placebo in combination with trastuzumab and pertuzumab as first-line maintenance therapy for HER2+ metastatic breast cancer. J Clin Oncol. 2026;44(17):1597-1607. doi:10.1200/JCO-25-02600
3. Swain SM, Miles D, Kim SB, et al. Pertuzumab, trastuzumab, and docetaxel for HER2-positive metastatic breast cancer (CLEOPATRA): end-of-study results from a double-blind, randomised, placebo-controlled, phase 3 study. Lancet Oncol. Published online March 12, 2020. doi:10.1016/S1470-2045(19)30863-0
4. FDA approves tucatinib for patients with HER2-positive metastatic breast cancer. US Food and Drug Administration. April 17, 2020. Accessed October 7, 2026.
