Final Overall Survival Analysis From PALOMA-2: Palbociclib Plus Letrozole in Advanced Breast Cancer

By: Justine Landin, PhD
Posted: Monday, February 12, 2024

A final overall survival analysis of the phase III PALOMA-2 trial indicated that the CDK4/6 inhibitor palbociclib plus the aromatase inhibitor letrozole did not significantly improve overall survival for patients with advanced breast cancer, according to Dennis J. Slamon, MD, PhD, of the David Geffen School of Medicine at the University of California Los Angeles, and colleagues. The updated findings of this randomized, double-blind, multicenter study were published in the Journal of Clinical Oncology.

“All the PALOMA trials demonstrated a statistically significant and clinically meaningful benefit with palbociclib plus endocrine therapy in the primary endpoint progression-free survival. Overall survival was a secondary endpoint in all PALOMA studies and was not significantly longer in the palbociclib arm of PALOMA-1, PALOMA-2, and PALOMA-3,” stated the study investigators.

Postmenopausal women with estrogen receptor–positive, HER2-negative breast cancer and no prior treatment for advanced disease were enrolled in PALOMA-2 (n = 666). All patients received 2.5 mg/d of letrozole. Patients were randomly assigned (2:1) to receive either palbociclib orally in 4-week cycles (125 mg/d) or matching placebo. Stratification factors included site of disease, any prior hormonal therapy, and disease-free interval from the end of treatment to disease recurrence.

At the median follow-up of 90.1 months, 23.3% of patients were still alive. Median overall survival was 53.9 months with palbociclib plus letrozole compared with 51.2 months with placebo plus letrozole (P = .34). Unknown survival outcomes were 13.3% with palbociclib vs 21.2% without it; recovered survival data indicated the median overall survival was 53.8 months and 49.8 months, respectively (P = .21).

“The long follow-up duration of the study, potential crossover affecting the longer survival for the control arm with multiple subsequent treatments poststudy, and an imbalance in the CDK4/6 inhibitor(s) use poststudy could represent potential confounders to overall survival results,” the study authors proposed.

Disclosure: For full disclosures of the study authors, visit ascopubs.org.

Journal of Clinical Oncology

---