Dr. Axe Wire · Study decoded · health

Breast Cancer Drug More Than Doubles Time Before Progression in Phase 3 Trial

A phase 3 trial of 551 women found trastuzumab rezetecan delayed cancer progression far longer than chemotherapy, though serious side effects were also more common.

By Dr. Josh Axe · October 30, 2026 · 1 source · Watch

A targeted antibody-drug conjugate called trastuzumab rezetecan more than doubled the time before advanced breast cancer progressed compared with standard chemotherapy, 16.4 versus 6.8 months, in a phase 3 trial of 551 women published October 23, 2026, in JAMA.

16.4 vs 6.8months PFS

551women, 73 hospitals

84% vs 68%severe side effects

The phase 3 trial enrolled 551 women ages 18 to 75 with ERBB2-low metastatic or unresectable locally recurrent breast cancer at 73 hospitals in China, randomizing them 1:1 between June 2023 and August 2025 to trastuzumab rezetecan (6.4 mg/kg by IV every three weeks, 277 women) or physician's choice of chemotherapy (274 women). At the March 2026 data cutoff, chemotherapy-naive patients went a median of 16.6 months without progression on the new drug versus 6.8 months on chemotherapy, and across the full study population the gap was 16.4 months versus 6.8 months. The benefit held whether or not the tumors were hormone receptor-positive.

ERBB2, also called HER2, is a protein on some breast cancer cells that can drive tumor growth. Trastuzumab rezetecan is an antibody-drug conjugate: an antibody that recognizes this protein carries a chemotherapy payload directly into cancer cells, potentially sparing healthy tissue compared with chemotherapy given throughout the body.

ERBB2-low tumors carry a smaller amount of this marker than classic HER2-positive cancers and have had fewer targeted options, so a drug built to recognize even low levels addresses a treatment gap. The progression-free survival gap, roughly two and a half times longer before the cancer progressed, is large for a head-to-head trial against standard chemotherapy.

Progression-Free Survival: New Drug vs Chemotherapy

JAMA, 2026, Fan et al.

The trial was open-label, so patients and doctors knew which treatment was given, which can influence reported outcomes. Overall survival was not reported, so it isn't yet known whether delaying progression means women live longer. Grade 3 or higher side effects were more frequent with the new drug, 84.1% (232 of 276) versus 67.9% (184 of 271) with chemotherapy, most commonly a drop in neutrophil count, an infection-fighting white blood cell, in 65.2% versus 54.2%.

Dr. Axe’s Take

This is a real delay in progression, but the trade-off matters: serious side effects ran higher on this drug than on chemotherapy, 84% versus 68%, led by a drop in neutrophils that raises infection risk. Delivering chemotherapy more precisely into cancer cells is a genuine engineering gain, but it doesn't address why the cancer developed, and this trial doesn't tell us whether women live longer. Anyone on this drug should track neutrophil counts and any fever or infection signs with their oncology team. Keep taking any prescribed medication, and make changes only with your prescriber, based on your numbers.

— Dr. Axe

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Study summary

Who: 551 women, ages 18-75, ERBB2-low advanced breast cancer, 73 hospitals in China
Design: Open-label, randomized phase 3 trial, enrolled June 2023-August 2025, followed to March 2026
Dose: Trastuzumab rezetecan 6.4 mg/kg IV every 3 weeks (n=277) vs physician's choice chemotherapy (n=274)
Primary result: Median progression-free survival 16.4 vs 6.8 months overall (hazard ratio 0.27)
Secondary: PFS in HR-negative disease: 16.5 vs 6.8 months; HR-positive disease: 16.4 vs 6.7 months
Funding / conflicts: Competing interests: Dr Xu reported receiving personal fees for consulting from Novartis and AstraZeneca outside the submitted work. No other disclosures were reported. Funding not reported in the abstract.
Date: Oct 23, 2026