Palbociclib plus an aromatase inhibitor as first-line therapy for metastatic breast cancer in US clinical practices: Real-world progression-free survival analysis

Abstract Background CDK4/6 inhibitor in combination with an aromatase inhibitor (AI) as initial endocrine therapy has become standard of care for patients with HR+/HER2– advanced/metastatic breast cancer (mBC). Large representative studies are needed to understand effectiveness of CDK4/6 inhibitor + AI in the real-world clinical setting. This study describes patient characteristics and real-world progression-free survival (rwPFS) in mBC patients treated with Palbociclib + AI in the first line setting. Methods The Flatiron longitudinal database contains information from 2 million cancer patients treated in the US from 275 cancer clinics. From this database, 878 HR+/HER2– mBC women treated with Palbociclib + AI as first-line therapy between February 2015 and August 2018 with at least 3 months of follow-up available were identified. Patients were followed from start of Palbociclib + AI therapy to November 2018, death, or last visit, whichever came first. rwPFS was defined as months from start of Palbociclib + AI to death or disease progression based on clinical assessment or radiographic progression with or without biopsy confirmation. Kaplan-Meier methods were used to estimate survival proportions in rwPFS. Results In our cohort of 878 eligible patients with a median follow-up of 19.4 months, 66.9% were white, mean age was 65.2 years, 50.8% had visceral disease (liver and/or lung involvement). Among these patients, 92.7% received Letrozole along with Palbociclib. Median rwPFS was 21.9 months (95%CI = 20.1 – 28.2). Table presents median rwPFS by subgroups. Conclusions These findings from a large cohort of patients in US routine clinical practices support first-line Palbociclib + AI therapy as standard of care for HR+/HER2- advanced/metastatic breast cancer. Table . 327P Real-world progression-free survival (rwPFS) by subgroups N Median rwPFS (months) 95%CI All patients 878 21.9 20.1 – 28.2 Age, year 18-64 407 21.8 18.8—26.4 65-74 294 21.4 16.1—29.9 ≥ 75 177 28.6 20.1—NE Ethnicity White 587 22.6 20.3—28.6 Black 62 NE 11.3—NE Asian 18 13.8 7.8—NE Hispanic 28 NE 5.9—NE Other/unknown 183 19.9 16.1—NE Menopausal status Premenopausal (Age≤50) 67 19.5 14.3—25.9 Postmenopausal (Age>50) 811 22.4 20.2—28.7 Disease stage at initial diagnosis 1 or 2 311 21.9 17.6—33.1 3 119 21.0 13.1—28.6 4 (De novo) 359 22.2 19.5—32.7 Unknown 89 26.5 15.5—NE ECOG Score 0 322 22.4 18.9—NE 1+ 225 21.0 16.5—28.3 No bone-only disease 623 17.3 14.6—20.2 Bone-only disease 255 NE NE Visceral disease 446 14.8 12.7—18.3 Nonvisceral disease 432 33.1 28.3—NE No# of metastic sites 1 352 NE NE 2 266 20.2 17.1—33.0 3+ 256 11.3 9.8—13.7 NE = not estimable Legal entity responsible for the study Pfizer Inc. Funding Pfizer Inc. Disclosure M. Torres: Full / Part-time employment: Emory University; Research grant / Funding (self): 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.