106P Palbociclib (PAL) in male patients (pts) with hormone receptor-positive/human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC): Pt characteristics and treatment (Tx) patterns from the POLARIS study

The prevalence of male breast cancer is <1% of all breast cancer cases, limiting the ability to conduct randomized clinical studies in this population. PAL plus an aromatase inhibitor or fulvestrant (FUL) is approved for the Tx of HR+/HER2– ABC in men. This analysis describes real-world pt characteristics and PAL use in male pts enrolled in the POLARIS study. POLARIS is an ongoing, prospective, real-world, noninterventional study in pts with HR+/HER2‒ ABC receiving PAL with a targeted enrollment of 1500 pts from ∼110 sites in the United States and Canada. Baseline demographics, clinical characteristics, and Tx patterns were descriptively analyzed in men with HR+/HER2– ABC using pt data collected from medical charts and physician surveys. A total of 15 men were enrolled at the data cutoff of December 17, 2020; median age was 66 years, 60.0% of pts had recurrent disease, 40.0% had de novo metastatic disease, and 46.7% had visceral disease (Table). PAL plus endocrine therapy (ET) was received as first-line (1L) therapy by 9 pts (60.0%), second-line (2L) therapy by 4 pts (26.7%), and 2L+ therapy by 2 pts (13.3%). Among all pts, 4 initiated PAL with letrozole, 3 with anastrozole, and 7 with FUL; 1 pt did not receive ET during cycle 1 but initiated FUL during cycle 2. PAL was initiated at 125 mg in 13 pts (86.7%) and 100 mg in 2 pts (13.3%). One pt had a dose modification (interruption due to pt decision).Table: 106PVariablen (%) (N=15)Age, yMedian (range)66 (43–82)RaceWhite14 (93.3)Black or African American1 (6.7)EthnicityNot Hispanic/Latino15 (100)Stage of current diagnosisLocally advanced (stage III)1 (6.7)Metastatic (stage IV)14 (93.3)Disposition of diagnosisRecurrent from earlier stage (stages 0–III)9 (60.0)De novo (newly diagnosed stage IV at enrollment)6 (40.0)Sites of distant metastases at ABC diagnosisMedian (range)2.5 (1.0–5.0)Bone metastases at ABC diagnosis among pts with stage IV diseaseBone only5 (41.7)Bone + other sites7 (58.3)Visceral diseaseYes7 (46.7)No8 (53.3)PAL starting dose, mg12513 (86.7)1002 (13.3) Open table in a new tab This is one of the first prospective trials to report pt characteristics and Tx patterns among male pts with HR+/HER2– ABC receiving PAL+ET. In this real-world population with a heavy disease burden, PAL was well tolerated with only 1 pt requiring dose modification. Most men received PAL+ET as 1L therapy and initiated PAL at the recommended dose of 125 mg. Further evaluation of Tx patterns in this population is warranted.