by Hope S. Rugo,
Xianchen Liu, Benjamin Li, Lynn McRoy, Rachel M. Layman, Adam Brufsky
The Breast: Published: March 27, 2023
Background
Palbociclib, the
first available cyclin-dependent kinase 4/6 inhibitor, plus endocrine therapy
is approved for hormone receptor-positive/human epidermal growth factor
receptor 2-negative (HR+/HER2-) metastatic breast cancer (MBC). This study
compared real-world effectiveness of palbociclib plus letrozole versus
letrozole in older patients with MBC in US clinical practice.
Methods
This retrospective
analysis included patients from the Flatiron Health longitudinal database.
Overall, 796 women with HR+/HER2- MBC aged ≥65 years starting palbociclib plus
letrozole or letrozole as first-line therapy between February 2015 and
September 2018 were included. Patients were evaluated from treatment start
until December 2018, death, or last visit, whichever came first. Real-world
progression-free survival (rwPFS), overall survival (OS), and real-world best
tumor responses (rwBTR) were endpoints. Stabilized inverse probability
treatment weighting (sIPTW) balanced patient characteristics.
Results
After sIPTW, 450
patients treated with palbociclib plus letrozole and 335 treated with letrozole
were included; median age was 74.0 years. Median rwPFS was 22.2 (95% CI,
20.0–30.4) months for palbociclib plus letrozole versus 15.8 (12.9–18.9) months
for letrozole (hazard ratio, 0.59 [0.47–0.74]; P < 0.001). Median OS
was not reached for palbociclib plus letrozole versus 43.4 months (30.0-not
estimable) with letrozole (hazard ratio, 0.55 [0.42–0.72]; P < 0.001).
No interactions between age groups (65–74 and ≥ 75 years) and treatment groups
were observed for rwPFS or OS. Rate of rwBTR was significantly higher for
palbociclib plus letrozole (52.4%) versus letrozole (22.1%; odds ratio, 2.0
[1.4–2.7]; P < 0.001).
Conclusion
This analysis
demonstrates the effectiveness of palbociclib combination therapy as
standard-of-care for older patients with HR+/HER2- MBC in the first-line
setting.
