Abstract P4-01-19: Real World Statistics on CDK4/6 Inhibitor Use in Metastatic Hormone Receptor Positive and HER2-Negative Breast Cancer with a Focus on Age
Authors: Monahan Kathleen , Kamaraju Sailaja , Cheng Yee Chung , Retseck Janet , Sriram Deepika , Burfeind John , Chitambar Christopher , Chaudhary Lubna N. 
Published: March 2023

Abstract
Background:
Combining CDK 4/6 inhibitors with hormone directed therapy using aromatase inhibitors (AI) or selective estrogen receptor down-regulators (SERD) is considered first line therapy for treatment of hormone receptor positive (HR+) human epidermal receptor 2 negative (HER2-) metastatic breast cancer (mBC). Here we aim to evaluate first line CDK 4/6 inhibitor practice patterns both nationally and locally (Wisconsin) in HR+ HER2- mBC patients and evaluate age as a potential factor impacting practice patterns.
Methods:
A retrospective analysis was performed utilizing IQVIA Anonymized Patient Longitudinal Data. The data base captures 60-85% of cancer patients across all 50 states in the United States and relies on diagnostic coding used in service or treatment claim filing. Patients queried were greater than 18 years old and were identified by a code indicating CDK4/6 inhibitor therapy or a combination of codes indicating mBC, HR+ status and HER- status. First line treatment was categorized as CDK4/6 inhibitor combination therapy, AI monotherapy, SERD, selective estrogen receptor modulator (SERM) monotherapy, chemotherapy, or other. Patients were further filtered by year, location, practice type (academic vs community), and age.
Results:
A total of 313,978 patients with mBC receiving first-line therapy were identified nationally between 2015 and 2021. The proportion of patients on first line CDK4/6 inhibitor combination therapy nationally significantly improved from 20% in 2015 (N=27,063) when palbociclib was first approved, to 53% in 2021 (N=54,023) (Table 1.) In 2021, first line use of CDK 4/6 inhibitor combination therapy was higher at 59% both in WI and our institution Froedtert Hospital and the Medical College of Wisconsin Cancer Center (Table 2.) At our center in 2021, the use of first line CDK4/6 inhibitor combination therapy in patients greater than age 65 was significantly lower at 35% (N=39) compared to patients less than 65 at 75% (N=64.) Further delineating the age groups at our center (Table 3,) use of CDK4/6 inhibitor combination therapy in patients aged 70-79 was 35% (N=20) and fell to 20% in patients greater than 80 in age (N=8.)
Conclusion:
Despite significant improvement in long-term outcomes with first line CDK4/6 inhibitor combination therapy in HR+ HER2- mBC patients, overall national usage is suboptimal. At our center, this was particularly apparent in patients older than 70. Identifying barriers to optimal use is critical to improve utilization of this important and effective class of drugs.
National Percentages of HR+ HER2- mBC Patients Stratified by First Line Treatment Between 2015-2021 HR+ HER2- mBC patients Nationally treated with first line therapy (N=313,978.)
National and Local Percentages of HR+ HER2- mBC Patients Stratified by First Line Treatment in 2021 HR+ HER2- mBC patients treated with first line therapy in 2021 Nationally (N=54,026,) in Wisconsin (N=694,) and at Froedtert Hospital and the Medical College of Wisconsin Cancer Center (N=103.)
Local Percentages HR+ HER2+ mBC Patients Stratified by First Line Treatment and Age Group HR+ HER2- mBC patients treated with first line therapy in 2021 at Froedtert Hospital and the Medical College of Wisconsin Cancer Center (N=103.)
Citation Format: Kathleen Monahan, Sailaja Kamaraju, Yee Chung Cheng, Janet Retseck, Deepika Sriram, John Burfeind, Christopher Chitambar, Lubna N. Chaudhary. Real World Statistics on CDK4/6 Inhibitor Use in Metastatic Hormone Receptor Positive and HER2-Negative Breast Cancer with a Focus on Age [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 P4-01-19.