Addition of Palbociclib Improves PFS in HR-Positive, HER2-Positive Metastatic Breast Cancer

MONDAY, Feb. 2, 2026 (HealthDay News) — For patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer, the addition of palbociclib to maintenance anti-HER2 and endocrine therapies leads to improved progression-free survival, according to a study published in the Jan. 29 issue of the New England Journal of Medicine.

In a phase 3 trial, Otto Metzger, M.D., from the Dana-Farber Cancer Institute and Harvard Medical School in Boston, and colleagues enrolled 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. Patients were randomly assigned to receive maintenance HER2-targeted and endocrine therapies with or without palbociclib (261 and 257 individuals, respectively).

The researchers found that patients in the palbociclib group had significantly longer progression-free survival than those in the standard-therapy group at a median follow-up of 53.5 months (median duration, 44.3 versus 29.1 months; hazard ratio for disease progression or death, 0.75). Grade 3 and 4 adverse events, mainly from neutropenia, occurred in 79.7 and 10.0 percent and 30.6 and 3.6 percent of patients, respectively, in the palbociclib and standard therapy groups.

“Every time we add a new medication to help improve outcomes, we also have to take into consideration the side effects that we might be seeing. So, we know that by adding this medication, we improve the amount of time that patients have on their first line of therapy,” Brittney Zimmerman, M.D., breast medical oncologist for the Northwell Health Cancer Institute, said in a statement. “But we also see that there”s a significant increase in lowering the white blood count and that many patients did have to reduce the dose of the medication. So, [we are] managing those side effects so that the regimens can be tolerable to patients because we want to make sure that we”re preserving quality of life and not just prolonging life.”

The study was funded by Pfizer, the manufacturer of palbociclib.

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