Abstract P4-01-31: High Incidence of Palbociclib Related Neutropenia in Asian Patients Associated with Genetic Polymorphisms

CDK4/6 inhibitors (CDK4/6i) is well established as the current standard of care for hormone positive (HR(+)) metastatic breast cancer (mBC), in combination with endocrine therapy. CDK4/6i extend a chemotherapy-free, progression free survival (PFS) that preserves quality of life in patients. The most common side effect of CDK4/6i is myelosuppression, with neutropenia the most prevalent adverse effect, especially for palbociclib and ribociclib. In PALOMA-2 and MONALEESA-2, where neutropenia was prevalent (any grade neutropenia 79.5%, grade 3/4 neutropenia 66.5% in PALOMA-2, and any grade neutropenia: 74.3%, grade 3/4 55.3% in MONALEESA-2), although febrile neutropenia seldom occurred (1.8%). Several studies have proposed different genetic factors predisposing to CDK4/6 inhibitor induced neutropenia, including Duffy antigen polymorphisms, ABCB1 and ERCC1 polymorphisms (ABCB1_rs1128503, ABCB1_rs1045642, ERCC1_rs11615, ERCC1_rs3212986), CDK6 polymorphisms, and others. Subgroup studies from the PALOMA trials have suggested that Asian patients receiving palbociclib have higher rates of neutropenia, although the exact explanation is unknown. We conducted a retrospective analysis of 102 Taiwanese patients who received palbociclib for HR(+) mBC at the Taipei Veterans General Hospital for the clinical features, incidence and time course of neutropenia were analyzed. Significant neutropenia incidence was observed (> 95% of all grade neutropenia, 74.5% grade 3/4 neutropenia). In addition, in our clinical cohort, one of the patients was a long term peritoneal dialysis patient newly diagnosed of HR(+) mBC and started on Palbociclib, initially 125mg, later decreased dosage to 100mg after neutropenia occurrence. By Liquid chromatography–mass spectrometry (LC–MS), we quantified the levels of palbociclib in her serum and peritoneal fluid at various time points, while on different dosage use. To our knowledge, this is the first pharmacokinetics analysis on a peritoneal dialysis patient receiving CDK4/6i. To investigate a possible genetic association for the high prevalence of neutropenia, we queried the Taiwan biobank, a nationwide biospecimen repository with 129,586 healthy individual genome wide DNA sequencing data deposited. We investigated the prevalence of the 4 SNPs previously reported to be related to neutropenia in the PALOMA studies. By comparing the Taiwan biobank data to SNP databases from different ethnicities, we observed interesting findings on ethnicity differences of SNP distribution and higher prevalence of neutropenia SNPs. Collectively, in this study we report real world data, biobank genome wide analysis, and a novel report of pharmacokinetic study in a peritoneal dialysis patient, providing novel insights into the real world use of palbociclib and CDKi. Table 1. Median TTF of each subsequent therapy after PAL+ET Characteristics of the clinical cohort treated with palbociclib at TVGH Citation Format: Kuan-Jung Huang, Ting-Hao Kuo, Ta-Chung Chao, Chun-Yu Liu, Yi-Fang Tsai, Chi-Cheng Huang, Ling-Ming Tseng, Cheng-Chih Richard Hsu, Jiun-I Lai. High Incidence of Palbociclib Related Neutropenia in Asian Patients Associated with Genetic Polymorphisms [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-01-31.