Real-world evidence of male breast cancer (BC) patients treated with palbociclib (PAL) in combination with endocrine therapy (ET).

1055 Background: The rarity of BC in men limits the feasibility of randomized clinical studies in this population. Treatment guidelines recommend that men with BC be treated similarly to postmenopausal women. PAL, a cyclin-dependent kinase 4/6 inhibitor, is used in men with metastatic BC (mBC) in real-world clinical practice, presenting an opportunity to utilize real-world evidence to enable healthcare providers to assess novel agents in this space. Methods: Two parallel approaches were taken. In the first approach, pharmacy and medical claims data from IQVIA Inc were retrospectively analyzed to describe the treatment patterns and duration of PAL + ET (aromatase inhibitor or fulvestrant) compared to ET in men with mBC. The second approach was a retrospective analysis of data derived from electronic health records in the Flatiron Health database to understand real-world clinical response to PAL + ET vs ET alone. Median duration of treatment (mDOT) was estimated by the Kaplan-Meier method. Results: Between Feb 2015 and Apr 2017, 12.9% (147/1139 [IQVIA dataset]) of men receiving treatment for mBC were prescribed PAL + ET for any line of therapy. The mDOT in the first-line setting was numerically longer in the PAL cohort (n=37) compared with the non-PAL cohort (n=214; 8.5 vs 4.3 mo, respectively). In particular, mDOT in the first-line setting was longer with PAL + letrozole (LET; n=26) than with LET alone (n=63; 9.4 vs 3.0 mo, respectively). In the Flatiron Health dataset between Feb 2015 and July 2017, the real-world maximum response rate in the PAL + ET cohort across all lines of therapy in the mBC setting (n=12) was 33.3% (2 complete responses [CR], 2 partial responses [PR]) vs 12.5% (0 CR, 1 PR) for the ET alone cohort (n=8). Conclusions: The real-world data sources used in this study support that men with mBC derive clinical benefit from the addition of PAL to ET. Given the challenges of conducting randomized clinical trials in men with mBC, noninterventional, real-world evidence data appear to be useful to delineate the benefit of such therapies in this setting. Funding: Pfizer.