Addition of CDK4/6 Inhibitor Benefits Patients With HR+, HER2+ Metastatic Breast Cancer, New Study Shows

The addition of a CDK4/6 inhibitor to standard therapy in patients with “double-positive” metastatic breast cancer significantly extended the time the disease did not progress according to data published in the New England Journal of Medicine. The final results of the phase 3 PATINA demonstrated that adding palbociclib to the current standard-of-care first-line maintenance therapy resulted in a more than 15-month improvement in progression-free survival in patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-positive (HER2+) metastatic breast cancer. The findings reported today were originally presented during a late-breaking oral session (Abstract GS2-12) at the 47th San Antonio Breast Cancer Symposium (SABCS) in December 2024.

Approximately 10% of all breast cancers are HR+, HER2+, which is sometimes referred to as double-positive or triple-positive breast cancer. Despite advances in treatment, the development of resistance to anti-HER2 and endocrine therapy is a challenge, and novel therapeutic approaches are needed for HR+, HER2+ metastatic breast cancer.

In the PATINA study, participants with metastatic disease who were previously treated with anti-HER2 therapy were randomized to receive palbociclib, in addition to anti-HER2 therapy and endocrine therapy, or anti-HER2 therapy and endocrine therapy alone. The primary endpoint was progression-free survival as assessed by the investigator. The median progression free survival was 44.3 months for patients treated with palbociclib in combination with anti-HER2 therapy (trastuzumab or trastuzumab plus pertuzumab) and endocrine therapy, and 29.1 months for patients treated with anti-HER2 therapy and endocrine therapy alone, representing an extension in median PFS of over 15 months.

Overall survival, a secondary endpoint, was not yet mature at the time of the analysis.

“This publication in the New England Journal of Medicine underscores the importance of these findings for the global breast cancer community,” said Otto Metzger, MD, Principal Investigator of PATINA and Associate Medical Director of International Strategic Initiatives at Dana-Farber Cancer Institute. “The ability to meaningfully extend progression-free survival with a well-tolerated regimen offers new hope for individuals living with this challenging subtype of metastatic breast cancer.”

The safety and tolerability of palbociclib in the PATINA study was consistent with its known safety profile in HR+, human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer, and no new safety signals were identified. The most common adverse events observed were hematologic toxicities, such as neutropenia and leukopenia. Non-hematologic adverse events included fatigue, stomatitis, and diarrhea, which were generally mild to moderate in severity.

PATINA is sponsored by Alliance Foundation Trials, LLC (AFT) in collaboration with six international cancer research groups in the U.S., France, Germany, Italy, Spain, Australia, and New Zealand. Funding support was provided by Pfizer.