In a phase II trial (PALMIRA) reported in the Journal of Clinical Oncology, Llombart-Cussac et al evaluated whether palbociclib rechallenge with second-line alternative endocrine therapy may improve progression-free survival vs second-line alternative endocrine therapy alone.
Study Details
In the international open-label trial, 198 patients progressing after first-line palbociclib plus endocrine therapy (aromatase inhibitor or fulvestrant) were enrolled between April 2019 and October 2022. Patients were randomly assigned 2:1 to receive palbociclib rechallenge plus second-line endocrine therapy (fulvestrant or letrozole; n = 136) or second-line endocrine therapy alone (n = 62). The primary endpoint was investigator-assessed progression-free survival.
Key Findings
Median follow-up for progression-free survival was 13.4 months. Median progression-free survival was 4.9 months (95% confidence interval [CI] = 3.6–6.1 months) in the palbociclib/endocrine therapy group vs 3.6 months (95% CI = 2.5–4.2 months) in the endocrine therapy group (hazard ratio [HR] = 0.84, 95% CI = 0.66–1.07, P = .149). Rates at 6 and 12 months were 42.1% vs 29.1% and 12.4% vs 12.3%, respectively.
Overall survival data were not mature at the time of analysis. Median overall survival was 28.3 months vs 28.8 months (HR = 1.06, 95% CI = 0.75–1.51).
Grade ≥ 3 adverse events occurred in 47.4% of the palbociclib/endocrine therapy group vs 10.0% of the endocrine therapy group. Only patients in the palbociclib/endocrine therapy group had grade 3 or 4 hematologic adverse events, including neutropenia (38.5%), leukopenia (3.7%), anemia (3.0%), and thrombocytopenia (0.7%).
The investigators concluded: “Palbociclib rechallenge plus an alternative [endocrine therapy] did not significantly improve [progression-free survival] compared with [endocrine therapy] alone in patients with hormone receptor–positive/HER2-negative [advanced breast cancer] progressing on a first-line palbociclib-based [endocrine therapy] regimen.”
Antonio Llombart-Cussac, MD, PhD, of Medica Scientia Innovation Research (MEDSIR), Barcelona, is the corresponding author of the Journal of Clinical Oncology article.
Disclosure: The study was supported by Pfizer. For full disclosures of all study authors, visit the Journal of Clinical Oncology.
