Giredestrant (oral SERD; ER degrader) + palbociclib misses 1L PFS significance vs letrozole + palbociclib in ER+/HER2– mBC

Giredestrant (GIRE) is a next-generation oral selective estrogen receptor antagonist/degrader (SERD) evaluated in the phase III, double-blind persevERA BC trial (NCT04546009) as first-line therapy with palbociclib (CDK4/6 inhibitor) versus standard letrozole (aromatase inhibitor) + palbociclib in ER+/HER2– locally advanced/metastatic breast cancer (n=992; 60.4% visceral; 19.1% de novo). At the 01/30/26 cutoff with 52.2-month median follow-up, investigator-assessed PFS numerically favored GIRE + palbociclib (median 33.1 vs 28.2 months; HR 0.89, 95% CI 0.76–1.05; p=0.1553), while OS was immature/neutral (HR 1.03; p=0.777) and ORR was similar (60.2% vs 58.8%); DoR trended longer with GIRE (38.5 vs 30.4 months; HR 0.80; p=0.056). Grade 3–4 AEs were largely palbociclib-typical hematologic toxicity, and endocrine-therapy discontinuation due to AEs was similar (6.5% vs 5.5); efficacy sits within the “good-AI+CDK4/6i” ballpark seen with other 1L CDK4/6 regimens (e.g., ribociclib + letrozole median PFS 25.3 months in MONALEESA-2; abemaciclib + AI PFS ~28.2 months in MONARCH 3), but without a statistically clear win over letrozole + palbociclib here.