Vepdegestrant, a PROTAC Estrogen Receptor Degrader, in Advanced Breast Cancer

Abstract Background Vepdegestrant is an oral proteolysis-Targeting chimera (PROTAC) estrogen receptor (ER) degrader that directly harnesses the ubiquitin-proteasome system. Methods In this phase 3, open-label, randomized trial, we enrolled patients with ER-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer who had received one previous line of cyclin-dependent kinase 4 and 6 inhibitor therapy plus one line of endocrine therapy (and up to one additional line of endocrine therapy). Patients were randomly assigned in a 1:1 ratio to receive vepdegestrant at a dose of 200 mg orally once every day of each 28-day cycle or fulvestrant at a dose of 500 mg, administered intramuscularly, on day 1 and day 15 of cycle 1 and on day 1 of subsequent cycles, with randomization stratified according to ESR1-mutation status and presence or absence of visceral disease. The primary end point was progression-free survival as assessed by blinded independent central review among the patients with ESR1 mutations and among all the patients who underwent randomization. Progression-free survival was estimated with Kaplan-Meier methods and hazard ratios with a stratified Cox proportional-hazards model. Results A total of 624 patients underwent randomization; 313 were assigned to receive vepdegestrant, and 311 to receive fulvestrant. Among the 270 patients with ESR1 mutations, the median progression-free survival was 5.0 months (95% confidence interval [CI], 3.7 to 7.4) with vepdegestrant and 2.1 months (95% CI, 1.9 to 3.5) with fulvestrant (hazard ratio, 0.58 [95% CI, 0.43 to 0.78]; P<0.001). Among all the patients, the median progression-free survival was 3.8 months (95% CI, 3.7 to 5.3) with vepdegestrant and 3.6 months (95% CI, 2.6 to 4.0) with fulvestrant (hazard ratio, 0.83 [95% CI, 0.69 to 1.01]; P=0.07). Adverse events of grade 3 or higher occurred in 23.4% of the patients in the vepdegestrant group and in 17.6% of the patients in the fulvestrant group. Adverse events led to treatment discontinuation in 2.9% and 0.7% of the patients, respectively. Conclusions Among patients with ER-positive, HER2-negative advanced breast cancer, vepdegestrant was associated with significantly longer progression-free survival than fulvestrant in the subgroup with ESR1 mutations but not in the full patient population.