Etcamah falls short in phase 3 trial of broader first-line use for advanced breast cancer

Clinical takeaway: These negative results do not support starting Etcamah broadly as first-line therapy for advanced breast cancer. The drug’s newly approved use is limited to patients whose tumors develop an ESR1 mutation during aromatase inhibitor plus CDK4/6 inhibitor treatment.

Etcamah (camizestrant) plus palbociclib did not significantly delay disease progression when used from the outset in a broad population with ER-positive, HER2-negative advanced breast cancer, according to topline results from the phase 3 SERENA-4 trial.

The finding comes just seven days after the FDA granted accelerated approval to camizestrant, an oral estrogen receptor degrader, combined with a CDK4/6 inhibitor. That approval was based on SERENA-6, which tested a different strategy. In that study, patients had already received an aromatase inhibitor plus a CDK4/6 inhibitor for at least six months. When a blood test detected an emerging ESR1 resistance mutation before imaging showed progression, the aromatase inhibitor was replaced with camizestrant. Switching to camizestrant reduced the risk of disease progression or death by 56%, with median progression-free survival of 16.0 months versus 9.2 months with continued aromatase inhibitor therapy.

By contrast, SERENA-4 enrolled 1,371 patients who had received no systemic treatment for advanced disease and did not require an emerging ESR1 mutation. Camizestrant plus palbociclib produced a numerical improvement over anastrozole plus palbociclib but missed the primary progression-free survival endpoint.

No efficacy estimates were released, preventing assessment of the size of the difference or whether particular subgroups benefited. No new safety concerns were identified, although detailed safety results also remain unavailable.

For now, the findings draw a clearer boundary around camizestrant’s role: biomarker-guided use after an ESR1 mutation emerges, rather than routine use from the beginning of first-line treatment. Full SERENA-4 results will be needed to determine whether any subgroups benefited from upfront therapy. Longer follow-up from SERENA-6 and FDA-required confirmatory studies will help establish whether the early treatment change produces lasting clinical benefit, including improved overall survival.

Source: AstraZeneca. (2026 Sep 11) Update on SERENA-4 Phase III trial of Etcamah in combination with palbociclib in upfront 1st-line advanced ER-positive breast cancer