Adding Palbociclib to Standard Adjuvant Endocrine Therapy for Estrogen Receptor–Positive Breast Cancer

By: Julia Fiederlein
Posted: Tuesday, October 25, 2022

Adding the CDK4/6 inhibitor palbociclib to standard adjuvant endocrine therapy did not improve outcomes in patients with stage IIA hormone receptor–positive, HER2-negative breast cancer, according to Angela DeMichele, MD, MSCE, of the University of Pennsylvania, Philadelphia, and colleagues. The preplanned analysis of the stage IIA cohort of the multicenter phase III PALLAS trial, which was presented in the October 2022 American Society of Clinical Oncology (ASCO) Plenary Series (Abstract 390216), suggested this combination may not reduce the incidence of early relapse in those with lower-stage disease. 

Between September 2015 and November 2018, a total of 1,010 patients with stage IIA disease were randomly assigned to receive the provider’s choice of adjuvant endocrine therapy for at least 5 years with or without 2 years of treatment with palbociclib. The protocol-defined number of events occurred at a median follow-up of 50 months.

Invasive disease–free survival events occurred in 6.2% and 8.9% of patients who received endocrine therapy with and without palbociclib, respectively; the 4-year rates of invasive disease–free survival did not seem to significantly differ between the arms (92.9% vs. 92.1%; hazard ratio = 0.75; P = .23). The investigators also observed nonsignificant differences for invasive breast cancer–free, distant recurrence–free, and locoregional cancer–free survival. No significant differences in invasive disease–free survival were reported in the subgroups stratified by age, receipt of chemotherapy, tumor grade, and clinical risk.

“Future analyses will incorporate genomic risk and other molecular patterns from the extensive transPALLAS correlative program,” the investigators concluded. “Additional follow-up is also underway to assess the impact of palbociclib exposure on late recurrence in hormone receptor–positive disease.”

Disclosure: For full disclosures of the study authors, visit coi.asco.org.

ASCO Plenary Series

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