NEJM Volume 394 Issue 17: April 30 2026 Analysis

Results from the phase III PATINA trial indicate that adding palbociclib to standard maintenance therapy significantly extends progression-free survival for patients with hormone receptor-positive (HR+), HER2-positive (HER2+) metastatic breast cancer.

The findings, published in the New England Journal of Medicine, show that the combination of palbociclib with anti-HER2 and endocrine therapies delayed disease progression in patients who had not progressed after receiving four to eight cycles of chemotherapy and HER2-targeted therapy.

Trial Design and Patient Outcomes

The international open-label trial enrolled 518 patients between June 2017 and July 2021. Participants were randomly assigned to two groups: 261 patients received maintenance anti-HER2 and endocrine therapy combined with palbociclib, while 257 patients received the standard maintenance therapy alone.

Patients in the palbociclib group received a daily dose of 125 mg for 21 days, followed by 7 days off, in 28-day cycles.

With a median follow-up of 53.5 months, the trial reported a median progression-free survival of 44.3 months for the palbociclib group, compared to 29.1 months for the standard therapy group.

The study observed varying estimated rates of progression-free survival at different intervals:

• At 12 months: 84.9% for palbociclib vs 73.2% for standard therapy
• At 24 months: 65.2% for palbociclib vs 55.3% for standard therapy
• At 48 months: 46.5% for palbociclib vs 38.3% for standard therapy

Objective response rates, excluding complete responses at the end of induction, were 32.9% in the palbociclib group and 24.8% in the standard therapy group. The median duration of these responses was 44.9 months and 30.8 months, respectively.

Safety and Adverse Events

The increase in progression-free survival was accompanied by a higher rate of toxicity. Grade 3 to 4 adverse events occurred in 79.7% of patients in the palbociclib group, compared to 30.6% in the standard therapy group.

Within the palbociclib group, grade 4 adverse events occurred in 10.0% of patients, while the standard therapy group saw grade 4 events in 3.6% of patients. Grade 5 adverse events were reported in 3.8% of the palbociclib group and 4.4% of the standard therapy group.

Neutropenia was the most common grade 3 or higher adverse event in the palbociclib group, affecting 60.5% of patients. No treatment-related deaths were observed during the trial.

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.

Investigators, New England Journal of Medicine

The study was funded by Pfizer and other organizations. Otto Metzger, MD, of the Dana-Farber Cancer Institute in Boston, served as the corresponding author for the research.