Early treatment utilization of palbociclib for metastatic breast cancer (MBC) in a U.S. community oncology network.

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e18112 Background: Palbociclib was approved in Feb 2015 as initial endocrine-based treatment (tx) for postmenopausal women with ER+/HER2- MBC. Efficacy and safety were assessed in an open-label randomized phase 2 trial. This study evaluated early usage patterns of palbociclib in a real world community oncology network. Methods: This is a retrospective observational longitudinal rolling cohort study to assess adult MBC patients (pts) initiating tx with palbociclib from 02/2015 to 01/2016. Data is cumulatively extracted from The US Oncology Network/McKesson Specialty Health electronic health record (EHR) database every 2 months. Pts on clinical trial are excluded. Demographic and clinical characteristics, prior tx, dosing patterns, and duration of tx are characterized. Results: 1148 pts were identified as having newly started palbociclib from 02/2015 to 09/2015. Median age at initiation of tx was 63 years. Among pts with documented receptor status (n = 623), 94% were ER+/HER2-. Median Karnofsky performance status at time of tx was 90%. The majority of pts had prior exposure to chemo (58%) or endocrine tx (85%) prior to palbociclib. Documented visceral metastases were present in 32% of pts and bone only metastases in 18%. 92% of pts started at the full dose of 125mg. Palbociclib was most frequently used in combination with letrozole (53%). Among pts with ≥ 1 CBC (n = 984), 39% and 6% of pts had neutrophil counts < 1000 and < 500 (grade 3 and grade 4), respectively. Among pts with at least 6 months of follow-up (n = 260), 31% had a dose reduction at any time, and 15% had discontinued tx. Conclusions: Early utilization demonstrates the demographic characteristics of pts receiving palbociclib appear similar to the US registrational trial. A higher proportion of pts had prior exposure to chemotherapy or endocrine tx in this community network, however line of therapy was not well captured using structured data. Proportion of pts with reduction in neutrophil counts to < 500 was consistent with what was observed in the clinical trial. Majority of the pts are still being treated with palbociclib. Additional planned follow-up time will provide further insight into the real world outcomes of tx. (Funding: Pfizer)

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