Real-world dosing patterns among metastatic breast cancer patients initiating first line (1L) palbociclib (PAL) therapy.

e13050Background: PAL was approved for the treatment (tx) of HR+/HER2- metastatic breast cancer (mBC) in combination (comb) with endocrine therapy (ET): aromatase inhibitors (AI) in 2015 and fulvestrant (FUL) in 2016, for patients (pts) who progressed on prior ET. We report the real-world dosing patterns of PAL in comb with ET as 1L therapy in mBC pts. Methods: Female mBC pts initiating PAL or ET monotherapy between 1/1/2012 and 3/31/2017 were selected from a linked EMR-claims database (EMR and Rx/medical claims). The first regimen observed following the diagnosis of mBC was defined as the 1L therapy (index date). The type of therapy used by the pt was determined by aggregating all applicable therapeutic drugs into comb regimens. Eligibility required 1L PAL+ET (letrozole, anastrozole, exemestaneor, FUL). Exclusions: pts with a second primary malignancy prior to index, or treated as part of a clinical trial, or with evidence of other regimen after mBC diagnosis. Pts were grouped as PAL+AI or PAL+FUL. Descr...