SABCS 2024: PADMA Compares First-Line Treatments in High-Risk Metastatic Breast Cancer

By: Celeste L. Dixon
Posted: Friday, December 13, 2024

In 120 patients with previously untreated, high-risk, hormone receptor (HR)-positive, HER2-negative metastatic breast cancer, the CDK4/6 inhibitor palbociclib plus endocrine therapy significantly improved the time to treatment failure and progression-free survival vs single-agent chemotherapy in the first-line setting, according to results of the phase III PADMA trial, presented at the 2024 San Antonio Breast Cancer Symposium (SABCS; Abstract LB1-03). A trend toward improved overall survival was also seen, according to Sibylle Loibl, MD, PhD, of the University of Frankfurt, Germany, and colleagues. According to the investigators, this study was the first to compare standard single-agent chemotherapy followed by maintenance endocrine therapy with a CDK4/6 inhibitor plus endocrine therapy as first-line therapy in this patient population.

The primary endpoint was met: Median time to treatment failure was significantly longer with palbociclib plus endocrine therapy (arm A)—17.2 months vs 6.1 months—than with single-agent chemotherapy (arm B, P = .0002). Also, after a median follow-up of 36.8 months, 45 patients (73.8%) in arm A vs 55 (93.2%) in arm B experienced a time-to-treatment failure event.

Safety was among the many secondary endpoints. Four patients (6.5%) in arm A and six (10.3%) in arm B experienced a serious treatment-related adverse event. Nonhematologic toxicity was similar as well, but hematologic toxicity was significantly higher in arm A.

The patients were treated at 28 German sites between 2018 and 2023. A total of 90 (75%) had metastases in two or more organ systems, 52 (43.3%) had symptomatic disease, and 10 (8.3%) were endocrine-resistant at enrollment; both were stratification factors. All patients were randomly assigned to receive either palbociclib plus endocrine therapy or single-agent chemotherapy of physician’s choice, the latter with or without following maintenance endocrine therapy.

Ultimately, the leading cause of treatment failure was disease progression (52.5% in arm A vs 76.3% in arm B). Median progression-free survival, another secondary endpoint, was significantly longer in arm A than in arm B (18.7 months vs 7.8 months; P = .0002).

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

2024 San Antonio Breast Cancer Symposium

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