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The approval of Enhertu as a second-line option further establishes the drug’s growing role in breast cancer, where it’s quickly becoming a go-to treatment for the roughly 15% of patients with HER2-positive disease.

First conditionally approved for third-line use in metastatic disease in 2019, Enhertu has now shown it may be able to help in additional settings. The new approval moves Enhertu forward into second-line care, where it’ll challenge Kadcyla — the drug it topped in head-to-head testing.

The green light also converts Enhertu’s earlier nod in third-line use to a “standard” approval, as the study helped confirm the findings underlying the drug’s original clearance, AstraZeneca said in a statement.

Enhertu’s fast momentum has already put pressure on Roche, which has multiple HER2-targeting medicines, as well as SeaGen and Macrogenics. Notably, Seagen lowered sales forecasts for its drug Tukysa because of emerging competition, mainly from Enhertu.

The medicine’s reach could grow larger still. Earlier this year, the drug kept disease from spreading and extended survival longer than doctors’ choice of chemotherapy in a Phase 3 study of breast cancer patients whose tumors express very little HER2. Up to 55% of breast cancer patients — including many with HR-positive tumors, the most common form of the disease — fit this description, and they’re currently ineligible to receive Kadcyla or other HER2-targeting drugs.

The study results, then, could precipitate a change in “the way we treat and categorize breast cancer,” Susan Galbraith, AstraZeneca’s head of oncology research and development, said in February. Details will be presented at the plenary session at the American Society of Clinical Oncology’s meeting next month, and they’ll be closely watched. Wall Street analysts are keeping an eye on whether the drug works in all-comers, or just in certain patients, as well as the frequency of a type of lung scarring known as interstitial lung disease — a known side effect of Enhertu and one that can require stringent monitoring to detect and manage.

The FDA has already granted Enhertu a breakthrough therapy designation in low expressors, a regulatory tool used to speed up drug reviews. It’s also under review in a type of lung cancer. Analysts expect sales, which totaled $214 million last year, to surge past $4 billion in 2026.

AstraZeneca separately reported two other positive study results on Thursday. Its diabetes drug, Farxiga, succeeded in a Phase 3 trial in a form of heart failure, matching data from Eli Lilly and Boehringer Ingelheim’s Jardiance, which was approved in that indication in February. Additionally, Ultomiris, a medicine AstraZeneca acquired when it bought Alexion, met its goals in a late-stage trial in neuromyelitis optica spectrum disorder, a rare autoimmune condition that can cause blindness and paralysis.