3599 - Comparative effectiveness of palbociclib plus letrozole vs letrozole for metastatic breast cancer in US real-world clinical practices

Background

Palbociclib, the first clinically available oral CDK4/6 inhibitor, in combination with endocrine therapy has become standard of care for HR+/HER2- advanced/metastatic breast cancer (MBC). No real-world studies have examined relative effectiveness of palbociclib plus endocrine therapy compared with endocrine therapy alone. This study compared real-world progression free survival (rwPFS) of palbociclib plus letrozole (PB+LE) vs letrozole alone (LE) for MBC in US routine clinical practices.

Methods

We conducted a retrospective analysis of MBC patients from the Flatiron Health longitudinal database, which contains electronic health records from 275 cancer clinics representing more than 2 million actively treated cancer patients in the US. Between February 2015 and August 2018, 1416 HR+/HER2– MBC women started PB+LE (n = 798) or LE (n = 618) as first-line therapy. Patients were evaluated from start of PB+LE or LE to November 2018, death, or last visit, whichever came first. rwPFS was defined as months from start of PB+LE or LE to death or disease progression based on clinical assessment or evidence by radiographic scan/tissue biopsy. 1:1 propensity score (PS) matching was used to balance patient characteristics.

Results

Of 1416 eligible patients, 906 were 1:1 PS matched (453 for each cohort). Median follow-up was 16.8 months, median age was 68.0 years, 70% were white, and 49.7% had visceral disease. Median rwPFS was 24.5 months (95%CI = 20.7 – 32.7) in PB+LE cohort and 17.1 months (95%CI=13.7—19.8) in LE cohort (HR = 0.68, 95%CI=0.56—0.84, p =.0003). Table presents key patient characteristics and landmark rwPFS rates.Table:

329P Patient characteristics and real-world progressionfree survival (rwPFS)

PB+LE = Palbociclib plus letrozole; LE = Letrozole alone; IQR = Interquartile Range

Conclusions

The first comparative analysis of a CDK4/6 inhibitor in combination with endocrine therapy compared to endocrine therapy alone provides real-world evidence confirming the findings of PFS benefit demonstrated in clinical trial data for palbociclib in diverse clinical practices.

Clinical trial identification

Editorial acknowledgement

Legal entity responsible for the study

Pfizer Inc.

Funding

Pfizer Inc.

Disclosure

R.M. Layman: Research grant / Funding (institution): Pfizer Inc. X. Liu: Shareholder / Stockholder / Stock options, Full / Part-time employment: Pfizer Inc. J. Mardekian: Shareholder / Stockholder / Stock options, Full / Part-time employment: Pfizer Inc. L. McRoy: Shareholder / Stockholder / Stock options, Full / Part-time employment: Pfizer Inc.