Abstract 236P
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). Little is known about effectiveness of palbociclib plus endocrine compared with endocrine therapy alone in older MBC patients. This study compared real-world progression free survival (rwPFS) and overall survival (OS) of palbociclib plus letrozole (PB+LE) vs letrozole alone (LE) in older MBC patients in US clinical practices.
Methods
We conducted a retrospective analysis of MBC patients from the Flatiron Health longitudinal database, which contains electronic health records from over 280 cancer clinics representing more than 2.2 million actively treated cancer patients in the US. Between February 2015 and February 2019, 796 HR+/HER2– MBC women aged ≥ 65 years started PB+LE or LE as first-line therapy. Patients were evaluated from start of PB+LE or LE to May 2019, 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 radiographic scan/tissue biopsy. Stabilized inverse probability treatment weighting (sIPTW) was used to balance patient characteristics.
Results
After sIPTW, 450 patients in PB+LE and 335 in LE were included. Median age was 74.0 years. Median rwPFS was 22.2 months (95%CI = 20.0-30.4) in PB+LE cohort and 15.8 months (95%CI=12.9-18.9) in LE cohort (HR=0.59, 95%CI=0.47-0.74, p <.0001). Median OS was not reached (NR) in PB+LE cohort vs 43.4 months (95%CI=30.0—NR) in LE cohort (HR=0.55, 95%CI=0.42-0.72, p <.0001). The table presents key patient characteristics and rwPFS and OS rates. Table: 236P
Patient characteristics and effectiveness outcomes after sIPTW (%)
| Variable | PB+LE (N=450) | LE alone (N=335) |
| 65-74 years | 51.4 | 52.3 |
| ≥75 years | 48.6 | 47.7 |
| White | 70.7 | 70.8 |
| Metastatic sites≥3 | 18.6 | 18.5 |
| Visceral disease | 38.3 | 38.7 |
| Bone only disease | 36.2 | 37.0 |
| rwPFS rate at 6 months | 86.0 | 75.7 |
| rwPFS rate at 12 months | 71.9 | 59.8 |
| rwPFS rate at 18 months | 58.6 | 45.1 |
| rwPFS rate at 24 months | 47.3 | 29.4 |
| OS rate at 24 months | 80.0 | 63.4 |
| OS rate at 36 months | 68.8 | 51.8 |
| Median follow-up, months | 20.2 | 18.6 |
PB+LE=Palbociclib plus letrozole; LE=Letrozole alone
Conclusions
This comparative analysis of PB+LE vs LE alone provides evidence of effectiveness for the palbociclib combination, supporting this treatment as a standard of care for older HR+/HER2- MBC patients in the first line setting.
Clinical trial identification
NCT04176354.
Editorial acknowledgement
Legal entity responsible for the study
Pfizer Inc.
Funding
Pfizer Inc.
Disclosure
H.S. Rugo: Financial Interests, Institutional, Research Grant: Pfizer Inc; Financial Interests, Institutional, Research Grant: Merck; Financial Interests, Institutional, Research Grant: Novartis; Financial Interests, Institutional, Research Grant: Lilly; Financial Interests, Institutional, Research Grant: Genentech; Financial Interests, Institutional, Research Grant: Odonate; Financial Interests, Institutional, Research Grant: Daiichi; Financial Interests, Institutional, Research Grant: Seattle Genetics; Financial Interests, Institutional, Research Grant: Eisai; Financial Interests, Institutional, Research Grant: Macrogenics; Financial Interests, Institutional, Research Grant: Sermonix; Financial Interests, Institutional, Research Grant: Boehringer Ingelheim; Financial Interests, Institutional, Research Grant: Polyphor; Financial Interests, Institutional, Research Grant: AstraZeneca; Financial Interests, Personal, Other, Honoraria: PUMA; Financial Interests, Personal, Other, Honoraria: Samsung; Financial Interests, Personal, Other, Honoraria: Mylan; Financial Interests, Institutional, Research Grant: Immunomedics. X. Liu, B. Li, L. McRoy: Financial Interests, Personal, Full or part-time Employment: Pfizer Inc; Financial Interests, Personal, Stocks/Shares: Pfizer Inc. R. Layman: Financial Interests, Institutional, Research Grant: Pfizer Inc; Financial Interests, Institutional, Research Grant: Novartis; Financial Interests, Institutional, Research Grant: Eli Lilly; Financial Interests, Personal, Advisory Board: Pfizer Inc; Financial Interests, Personal, Advisory Board: Eli Lilly; Financial Interests, Personal, Advisory Board: Novartis; Financial Interests, Institutional, Research Grant: Zentalis; Financial Interests, Institutional, Research Grant: Celcuity. A. Brufsky: Financial Interests, Personal, Advisory Role: Pfizer Inc; Financial Interests, Personal, Advisory Role: AstraZeneca; Financial Interests, Personal, Advisory Role: Sanofi; Financial Interests, Personal, Advisory Role: Eli Lilly; Financial Interests, Personal, Advisory Role: Novartis.