Real-world data support first-line palbociclib plus an aromatase inhibitor (AI) as standard care for hormone receptor (HR)-positive, HER2-negative metastatic breast cancer, according to researchers.

The data showed that palbociclib plus AI treatment improves progression and survival outcomes when compared with AI treatment alone, outside the clinical trial setting. These findings were presented in a poster at JADPRO Live 2022, the annual APSHO meeting.

The study included 2888 patients in the Flatiron Health longitudinal database treated from February 3, 2015, to March 31, 2020. The patients had HR-positive, HER2-negative metastatic breast cancer. The cohort included men and postmenopausal women starting first-line treatment.


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A total of 1324 patients received palbociclib plus an AI, and 1564 patients received an AI alone. At baseline, the median age was 67 years in the palbociclib-AI group and 72 years in the AI-alone group. Roughly 99% of patients in both groups were women, and about 68% of patients in each group were White.

Visceral metastasis was seen in 33.5% of patients in the palbociclib-AI group and 25.8% of patients in the AI-alone group. Rates of bone-only metastasis were 39.2% and 38.3%, respectively, and rates of brain metastasis were 2.0% and 3.2%, respectively.

Patients were evaluated from the start of treatment until September 30, 2020, death, or their last visit, whichever came first. The study’s primary endpoint was overall survival (OS), and the secondary endpoint was real-world progression-free survival (rwPFS).

In an unadjusted analysis, the median OS was 53.4 months in the palbociclib-AI group and 40.4 months in the AI-alone group (hazard ratio [HR], 0.67; 95% CI, 0.60-0.76; P <.0001). The median rwPFS was 19.8 months with palbociclib-AI and 13.9 months with AI alone (HR, 0.68; 95% CI, 0.62-0.76; P <.0001).

When the researchers used stabilized inverse probability treatment weighting to balance patient characteristics, outcomes remained superior with palbociclib. The median OS was 49.1 months in the palbociclib-AI group and 43.2 months in the AI-alone group (HR, 0.76; 95% CI, 0.65-0.87; P =.0001). The median rwPFS was 19.3 months and 13.9 months, respectively (HR, 0.70; 95% CI, 0.62-0.78; P <.0001).

Outcomes were superior with palbociclib when the researchers used propensity score matching to balance patient characteristics as well. The median OS was 57.8 months in the palbociclib-AI group and 43.5 months in the AI-alone group (HR, 0.72; 95% CI, 0.62-0.83; P <.0001). The median rwPFS was 19.8 months and 14.9 months, respectively (HR, 0.72; 95% CI, 0.63-0.82; P <.0001).

The researchers concluded that the results of this study, which is the largest of its kind, support first-line palbociclib plus an AI as a standard of care for patients with HR-positive, HER2-negative metastatic breast cancer.

Disclosures: This study was sponsored by Pfizer, Inc. Poster presenter Rachael McCaleb, PharmD, is employed by the company. Poster author Hope S. Rugo, MD, disclosed affiliations with Pfizer, Merck, Novartis, Eli Lilly, Roche, Daiichi-Sankyo, Seattle Genetics, Macrogenics, Sermonix, Boehringer Ingelheim, Polyphor, AstraZeneca, Ayala, Gilead, Astellas, PUMA, and Samsung. No other authors disclosed conflicts of interest.

Reference

Rugo HS, Brufsky A, Liu X, et al. Overall survival with first-line palbociclib plus an aromatase inhibitor (AI) vs AI in metastatic breast cancer: A large real-world database analysis. Poster presented at: JADPRO Live 2022; October 20-23, 2022; Aurora, CO. Abstract JL1022E.