In a phase III trial (PATINA) reported in The New England Journal of Medicine, Metzger et al found that the addition of palbociclib to anti-HER2 and endocrine therapies significantly prolonged progression-free survival in patients with hormone receptor–positive, HER2-positive metastatic breast cancer who did not have disease progression after four to eight cycles of chemotherapy plus HER2-targeted therapy.
Study Details
In the international open-label trial, 518 patients were randomly assigned between June 2017 and July 2021 to receive maintenance anti-HER2 therapy and endocrine therapy (standard therapy) with (n = 261) or without (n = 257) palbociclib at 125 mg daily for 21 days on/7 days off in 28-day cycles. The primary endpoint was investigator-assessed progression-free survival.
Key Findings
Median follow-up was 53.5 months.
Median progression-free survival was 44.3 months (95% confidence interval [CI] = 32.4–56.8 months) in the palbociclib group vs 29.1 months (95% CI = 23.3–38.6 months) in the standard therapy group (hazard ratio [HR] = 0.75, 95% CI = 0.59–0.96, P = .02). Estimated rates at 12, 24, and 48 months were 84.9% vs 73.2%, 65.2% vs 55.3%, and 46.5% vs 38.3%, respectively.
Objective response (excluding complete responses at the end of induction) was observed in 32.9% vs 24.8% of patients, with median response durations of 44.9 vs 30.8 months. At data cutoff, death had occurred in 60 vs 63 patients (HR = 0.86, 95% CI = 0.61–1.23).
Grade 3 to 4 adverse events occurred in 79.7% of the palbociclib group (grade 4 in 10.0%) vs 30.6% of the standard therapy group (grade 4 in 3.6%). Grade 5 adverse events occurred in 3.8% vs 4.4% of patients. The most common grade ≥ 3 adverse event in the palbociclib group was neutropenia (60.5%). No treatment-related deaths were observed.
The investigators concluded: “The addition of palbociclib to maintenance anti-HER2 and endocrine therapies led to a significant improvement in progression-free survival over standard therapy, with increased toxic effects, mainly neutropenia.”
Otto Metzger, MD, of Dana–Farber Cancer Institute, Boston, is the corresponding author for The New England Journal of Medicine article.
DISCLOSURE: The study was funded by Pfizer and others. For full disclosures of the study authors, visit nejm.org.
