Abstract P5-14-08: Effectiveness of palbociclib plus letrozole vs letrozole in US Hispanic and African American patients with metastatic breast cancer: Flatiron database analysis
Authors: Rugo Hope , Lynce Filipa , Liu Xianchen , Li Benjamin , McRoy Lynn , Isaacs Claudine 
Published: March 2022

Background Palbociclib, the first clinically available oral CDK4/6 inhibitor, in combination with endocrine therapy has been approved for HR+/HER2- advanced/metastatic breast cancer (MBC) in the US for more than 6 years. Although clinical trials and growing real-world data have demonstrated safety and effectiveness of palbociclib plus endocrine therapy, data on treatment patterns and effectiveness of palbociclib in minority patients with MBC are limited. This study compared real-world progression free survival (rwPFS) and overall survival (OS) of palbociclib plus letrozole (PB+LE) vs letrozole alone (LE) in Hispanic and African American patients with HR+/HER2- MBC in US routine clinical practices. Methods We conducted a retrospective analysis of patients with MBC 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, 151 Hispanic and African American women with HR+/HER2- MBC started PB+LE or LE as first-line therapy. Patients were evaluated from start of PB+LE or LE to May 31, 2019 (Data cutoff date), death, or last visit, whichever came first. rwPFS was defined as months from start of PB+LE or LE to death or disease progression, evaluated based on clinical assessment or radiographic scan/tissue biopsy. Cox proportional-hazards models were used to estimate the relative effectiveness of PB+LE vs LE without and with adjustment of baseline demographics and clinical characteristics. Results Of the 151 eligible patients, 114 (75.5%) were African American, 37 (24.5%) were Hispanic, 76 (50.3%) were treated with PB+LE, and 75 (49.7%) were treated with LE. Median age was 64.5 years in PB+LE patients and 69.0 years in LE patients, respectively. Median follow-up was 2 months longer in PB+LE patients than LE patients (21.7 vs 19.4 months). PB+LE patients were more likely to have ≥2 metastatic sites than LE patients (42.1% vs 34.6%). Median rwPFS was 20.0 months (95%CI = 12.3 - NR) in PB+LE patients and 7.0 months (95%CI=4.6-9.5) in LE patients (HR=0.38, 95%CI=0.25-0.58, p &lt;0.0001; Adjusted HR=0.45, 95%CI=0.25-0.80, p =0.006). Median OS was not reached (NR, 95%CI=(33.6-NR)) in PB+LE patients vs 24.0 months (95%CI=17.1-NR) in LE patients (HR=0.45, 95%CI=0.27-0.77, p =0.004; Adjusted HR=0.84, 95%CI=0.41-1.74. p=0.646). Similar results were observed in African American patients only. Table 1 presents key patient characteristics and rwPFS and OS results. Conclusions This exploratory comparative analysis of palbociclib plus letrozole compared to letrozole alone provides evidence that first-line palbociclib in combination with endocrine is effective for Hispanic and African American HR+/HER2- MBC patients in the real-world setting. Further research with more patients and longer follow-ups is warranted in minority MBC patients.

Table. Patient characteristics and effectiveness outcomesVariablePB+LE(N=76)LE alone(N=75)African American, n (%)54 (71.1)60 (80.0)Hispanic, n (%)22 (28.9)15 (20.0)Median age (IQR), years64.5(58.5-71.0)69.0 (59.0-80.0)Metastatic sites≥2, n (%)32 (42.1)26(34.6)Visceral disease, n (%)29 (38.2)29 (38.7)Bone only disease, n (%)29 (38.2)26 (34.7)rwPFS rate at 6 months, %78.052.9rwPFS rate at 12 months, %61.629.4rwPFS rate at 20 months, %49.016.3Median PFS (95%CI), months20.0(12.3-NR)7.0 (4.6-9.5)OS rate at 12 months, %89.373.0OS rate at 24 months, %72.648.7Median OS (95%CI), months24.01 (17.1-NR)NR (33.6-NR)Median follow-up, months (IQR)21.7 (15.3-32.9)19.4 (8.9-30.7)PB+LE= Palbociclib plus letrozole; LE= Letrozole alone; IQR= Interquartile range; NR= Not reached; OS= Overal surval; rwPFS = real-world progression free survival

Citation Format: Hope Rugo, Filipa Lynce, Xianchen Liu, Benjamin Li, Lynn McRoy, Claudine Isaacs. Effectiveness of palbociclib plus letrozole vs letrozole in US Hispanic and African American patients with metastatic breast cancer: Flatiron database analysis [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-14-08.