FDA approves Pfizer's TUKYSA as first-line maintenance treatment for HER2+ metastatic breast cancer

The FDA has approved Pfizer's Tukysa in combination with trastuzumab and pertuzumab as a first-line maintenance treatment for HER2-positive metastatic breast cancer. Based on the Phase 3 HER2Climb-05 trial of 654 patients, the regimen reduced the risk of disease progression or death by 35.9%, extending median progression-free survival by 8.6 months to 24.9 months. However, the drug's label now carries a boxed warning for severe hepatotoxicity, following a 3.9% rate of serious liver toxicity and one fatal case in the trial. The approval expands Tukysa's market to earlier-stage patients, positioning Pfizer to challenge AstraZeneca and Daiichi Sankyo's dominant therapy, Enhertu.

FDA approvals of Tukysa

• ▪The FDA approved Pfizer's Tukysa on October 7, 2026, in combination with trastuzumab and pertuzumab, as a first-line, chemotherapy-free maintenance treatment for adults with unresectable locally advanced or metastatic HER2-positive breast cancer following induction therapy.
• ▪The FDA first approved Tukysa in April 2020 in combination with trastuzumab and capecitabine for patients with advanced unresectable or metastatic HER2-positive breast cancer who had received prior anti-HER2 regimens.

Efficacy of Tukysa in the HER2Climb-05 trial

• ▪The overall survival data from the HER2Climb-05 trial, which is a key secondary endpoint, has not yet been finalized and remains immature.
• ▪The HER2Climb-05 trial randomized 654 participants who had completed induction therapy of trastuzumab, pertuzumab, and a taxane with no evidence of disease progression.
• ▪In the phase 3 HER2Climb-05 trial, adding Tukysa to trastuzumab and pertuzumab reduced the risk of disease progression or death by 35.9% compared to placebo and the two drugs alone.
• ▪The HER2Climb-05 trial showed a median progression-free survival of 24.9 months for the Tukysa arm compared to 16.3 months for the placebo arm, representing an 8.6-month extension.

Hepatotoxicity risks of Tukysa

• ▪The FDA-approved label for Tukysa carries a boxed warning for severe hepatotoxicity, which was more severe in the HER2Climb-05 trial than in the drug's previously known safety profile.
• ▪Hepatotoxicity in the HER2Climb-05 trial led to Tukysa dose reductions in 15% of patients and permanent discontinuation of the drug in 8% of patients.
• ▪There were five confirmed Hy's Law cases in the HER2Climb-05 trial, all of which occurred following a rechallenge with Tukysa.
• ▪In the HER2Climb-05 trial, serious hepatotoxicity affected 3.9% of patients in the Tukysa treatment arm, including one fatal case of drug-induced liver injury.

Pfizer's first-line approvals

• ▪The October 7, 2026, approval of Tukysa marked Pfizer's second HER2 first-line approval in less than four months.
• ▪The first-line approval of Tukysa is expected to open the drug up to a larger patient pool earlier in their disease course, potentially extending the duration of treatment.

Market competition for HER2-positive breast cancer treatments

• ▪In June 2026, Pfizer secured a frontline maintenance approval for its CDK4/6 inhibitor Ibrance in combination with Herceptin for hormone receptor-positive, HER2-positive breast cancer.
• ▪The frontline maintenance approvals of Tukysa and Ibrance create competition for AstraZeneca and Daiichi Sankyo's antibody-drug conjugate Enhertu, which dominates the HER2 treatment landscape.

Tukysa sales and revenue

• ▪Pfizer acquired Tukysa through its $43 billion buyout of Seagen in 2023, with global revenue for the drug shrinking from $480 million in 2024 to $463 million in 2025.
• ▪Analysts initially projected that peak sales for Tukysa would reach $1.2 billion by 2030.

Prevalence and prognosis of HER2-positive breast cancer

• ▪HER2 is overexpressed in an estimated 15% to 20% of breast cancer cases and is associated with a poorer prognosis.
• ▪The 5-year survival rate for HER2-positive metastatic breast cancer is estimated at 41% to 47% depending on hormone receptor status.

Debatable claims

• ▪Transitioning patients from Enhertu to Tukysa maintenance is premature without clinical trial data
• ▪Progression-free survival is an adequate basis for approving first-line cancer maintenance therapies
• ▪Tukysa's progression-free survival benefit justifies its severe hepatotoxicity risks