Palbociclib plus letrozole is associated with improved outcomes compared to letrozole alone for the first-line treatment of patients with HR-positive, HER2-negative metastatic breast cancer with lung or liver metastases, according to results from a real-world study presented at the 2021 San Antonio Breast Cancer Symposium.

This study, by Adam Brufsky, MD, Comprehensive Breast Cancer Center, University of Pittsburgh Medical Center, Pittsburgh, PA, et al, aimed to compare real-world progression free survival (rwPFS) and overall survival (OS) with palbociclib plus letrozole vs letrozole alone in HR-positive, HER2-negative breast cancer with lung or liver metastases in routine clinical practice in the United States.

The Flatiron Health longitudinal database was used to identify 551 with HR-positive, HER2-negative breast cancer with lung or liver metastases patients who started palbociclib plus letrozole or letrozole alone as first-line therapy between February 2015 and February 2019. Patients were evaluated from start of first-line therapy to May 31, 2019, death, or last visit.

Cox proportional-hazards models with and without adjustment for baseline demographics and clinical characteristics were used to estimate the relative effectiveness of palbociclib plus letrozole vs letrozole alone.

Of the 551 patients included in the study, 353 (64.1%) had lung metastases, 123 (22.3%) had liver metastases, and 75 (13.6%) had both. Overall, 330 (59.9%) patients were treated with palbociclib plus letrozole and 221 (40.1%) were treated with letrozole alone.

The median age of patients treated with combination therapy was 66 years and those treated with letrozole monotherapy was 71 years. Patients treated with combination therapy were more likely to have ≥3 metastatic sites than those treated with letrozole alone (43.9% vs 37.1%, respectively).

Median follow-up was 22.6 months in the palbociclib plus letrozole arm and 22.1 months in the letrozole alone arm. Median rwPFS was 15.4 months vs 10.2 months, respectively (HR = .60, 95% CI = .49-.74; P <.0001; Adjusted HR = .56, 95% CI = .45-.71; P <.0001). In addition, media OS was note reached and 29.4 months, respectively (HR = .56, 95% CI = .43-.74; P <.0001; Adjusted HR = .61, 95% CI = .45-.82; P <.0001).

“This real-world comparative analysis provides evidence that palbociclib in combination with letrozole is associated with improved outcomes compared to letrozole alone for HR+/HER2- MBC [metastatic breast cancer] patients with lung or liver metastases in the first-line setting,” concluded Dr Brufsky and colleagues.

Brufsky A, Liu X, Li B, et al. Real-world effectiveness of palbociclib plus letrozole vs letrozole alone for metastatic breast cancer with lung/liver metastases: Flatiron database analysis. Presented at: 2021 San Antonio Breast Cancer Symposium; December 7-10, 2021; virtual. Abstract P1-18-20.