ASCO 2026: Evaluating Giredestrant in First-Line ER+/HER2- Metastatic Breast Cancer

Highly anticipated data from the phase 3 persevERA trial were presented at the 2026 American Society of Clinical Oncology Annual Meeting (ASCO 2026) by Dr. Nicholas Turner, of The Royal Marsden Hospital. The current frontline treatment for ER-positive/HER2-negative locally advanced or metastatic breast cancer is a combination of a CDK4/6 inhibitor (such as palbociclib, ribociclib, or abemaciclib) paired with an aromatase inhibitor (like letrozole or anastrozole). 

While this combination has dramatically extended survival over the past decade, almost all patients eventually develop resistance to therapy. Often, this resistance is driven by mutations in the ESR1 gene. In persevERA, giredestrant, a potent, oral selective estrogen receptor degrader (SERD) that achieves robust ER occupancy and is active regardless of ESR1 mutation status was evaluated in combination with palbociclib. It was a double-blind, placebo-controlled, randomized, multicenter phase 3 study designed to evaluate the efficacy and safety of frontline giredestrant  plus palbociclib in patients with ER-positive/HER2-negative locally advanced or metastatic breast cancer.

persevERA Study Design

Treatment-naïve patients were randomized in a 1:1 ratio to receive either giredestrant (30 mg PO) plus letrozole placebo once daily or letrozole (2.5 mg PO) plus giredestrant  placebo once daily on Days 1-28 of each 28-day cycle, with palbociclib (125 mg PO once daily) on Days 1-21 of each 28-day cycle [Figure 1].  Men and premenopausal women received luteinizing hormone-releasing hormone agonist.  

Figure 1. Study Schema

Results of the persevERA Trial

With a median follow-up period of 52.2 months and encompassing 623 progression-free survival (PFS) events, there was a 4.9-month absolute improvement in median PFS for patients in the giredestrant arm (33.1 months) compared with those receiving letrozole (28.2 months). Despite this clinical extension, the improvement did not reach the study’s predefined threshold for statistical significance (HR, 0.89; 95% CI, 0.76–1.05; P = .156) [Figure 2]. 

Figure 2.Progression Free Survival

Furthermore, median overall survival data remains immature and is not yet evaluable for either cohort, with current analyses showing no statistically significant difference between the two treatment groups (HR, 1.03; 95% CI, 0.83–1.28; P = .777) [Figure 3].

Figure 3. Overall Survival

Efficacy analyses demonstrated comparable outcomes between the two treatment regimens, with objective response rates of 60.2% for the giredestrant plus palbociclib combination and 58.8% for letrozole plus palbociclib. Clinical benefit rates closely aligned as well, reaching 82.6% and 82.1%, respectively. While the median duration of response showed a favorable trend for the giredestrant cohort—lasting 38.5 months compared with 30.4 months with letrozole—this extension narrowly missed statistical significance (HR, 0.80; 95% CI, 0.63–1.01; P = .056). Both combinations exhibited safety profiles consistent with their established toxicities, featuring low and equivalent rates of endocrine therapy discontinuation because of adverse events. Ultimately, investigators concluded that although giredestrant plus palbociclib offered a numerical PFS advantage, it did not demonstrate significant superiority over the letrozole regimen as a first-line therapy. 

Clinical Implications

Despite persevERA not meeting its primary end point in ER-positive/HER2-negative locally advanced, metastatic breast cancer, the clinical trajectory for giredestrant remains highly promising. Giredestrant has already established superiority over standard endocrine therapies in both the adjuvant setting, demonstrated by the lidERA trial, and following progression on CDK4/6 inhibitors, as seen in the evERA trial. Moving forward, clinical focus is strategically pivoting toward higher-risk, endocrine-resistant patient populations that require more profound receptor degradation. To this end, the ongoing phase 3 pionERA trial is actively evaluating giredestrant against the injectable SERD fulvestrant in patients who have relapsed on adjuvant therapy. Ultimately, while the persevERA results may not alter standard first-line prescribing practices in the immediate future, they have provided the oncology community with crucial insights into the most effective clinical sequencing and optimal deployment of next-generation SERDs to maximize patient benefit.

Reference

1. Turner NC, Jhaveri KL, Bardia A, et al. Giredestrant (GIRE) + palbociclib (PALBO) vs letrozole (LET) + PALBO as first-line (1L) therapy in patients (pts) with estrogen receptor–positive, HER2-negative locally advanced or metastatic breast cancer (ER+, HER2– LA/mBC): Primary analysis of the phase III persevERA BC trial. J Clin Oncol. 2026;44(17 suppl). doi:10.1200/JCO.2026.44.17_suppl.LBA1006