Dr Mardones on Giredestrant’s Numerical PFS Edge in Advanced Breast Cancer

Primary findings from the phase 3 persevERA BC trial, presented at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting, evaluated the efficacy of combining giredestrant and palbociclib as a first-line treatment for patients with estrogen receptor–positive (ER+), HER2-negative locally advanced or metastatic breast cancer.

The trial compared an experimental regimen of giredestrant (an oral selective estrogen receptor degrader, or SERD) plus palbociclib (a CDK4/6 inhibitor) against a standard control arm of letrozole plus palbociclib. With a median follow-up of just over 52 months for both arms, the study met its primary end point of investigator-assessed progression-free survival (INV-PFS) by demonstrating a numerical benefit, though it failed to achieve pre-specified statistical significance. The median INV-PFS was 33.1 months for the giredestrant combination compared to 28.2 months for the letrozole combination, yielding a hazard ratio of 0.89. The trial had been powered to detect a more pronounced hazard ratio of 0.77.

Secondary end points showed similar trends. An early, immature analysis of overall survival revealed no significant difference between the two groups, with median survival not yet reached in either arm. The objective response rate and clinical benefit rate were nearly identical, sitting at roughly 60% and 82%, respectively. However, the duration of response was numerically longer in the giredestrant group at 38.5 months compared to 30.4 months in the letrozole group.

Safety profiles were manageable and consistent with previous studies. Grade 3/4 adverse events occurred in 85.5% of the giredestrant group and 80.8% of the letrozole group, though treatment discontinuation rates remained low and comparable. Notably, asymptomatic, low-grade bradycardia (slow heart rate) was significantly more common with giredestrant (11.7% vs 1.8%). Researchers noted that further trials, such as the ongoing phase 3 pionERA BC trial, will help clarify which patient subgroups benefit most from giredestrant.