(013) Assessing Adherence of Cyclin-Dependent Kinase 4 and 6 Inhibitors in Patients with Hormone Receptor-Positive Breast Cancer: a Retrospective Observational Study

Poster Abstract:

Introduction:
Cyclin dependent kinase 4/6 inhibitors (CDK 4/6i) combined with endocrine therapy (ET) are used to treat hormone receptor-positive, HER2-negative (HR+/HER2-) high-risk early-stage and advanced stage/metastatic breast cancer (mBC). The combination CDK 4/6i with ET have significantly increased progression-free and overall survival compared to ET alone in mBC patients, and the combination has improved invasive disease-free survival and distant relapse-free survival in patients with high-risk early-stage.1-4 Non-adherence to anti-cancer drugs have shown to increase the risk of disease progression in patients.5 Therefore, it is important to monitor and improve adherence to this life-saving treatment combination in patients.

Objective:
The purpose of this retrospective study was to assess medication adherence to CDK4/6i’s in patients with HR+/HER2- breast cancer (BC) and identify factors associated with non-adherence at a large hospital system.

Methods:
In our retrospective, observational study, data was collected from Houston Methodist patients with HR+/HER2- BC with available medication fill history utilizing Epic electronic medical records. The primary endpoint was medication adherence of up to 18 months (January 2022 through June 2023) that was calculated as the mean procession ratio (MPR). Patients were considered adherent with the MPR of at least 80%. The MPR was determined separately for palbociclib’s and ribociclib’s 21-day course and abemaciclib’s 28-day course. Differences in adherent and non-adherent groups of patients was evaluated using the student’s t-test for continuous variables in patient characteristics and chi-squared tests for categorical variables.

Results:
A total of 61 patients were assessed and analyzed. Majority of the patients were Caucasian (61%), not Hispanic or Latino (80%), and postmenopausal (62%). About 70% of the patients were on abemaciclib, 25% were on palbociclib, and 5% were on ribociclib. There were more patients on aromatase inhibitors (89%) than fulvestrant (10%) and tamoxifen (2%). Out of the 61 patients, 32 patients (52%) were considered adherent. Of the patients who were adherent, 91% were on abemaciclib, 9% were on palbociclib, and no patients were on ribociclib. Patients greater than 60 years old were more likely to be non-adherent to their CDK4/6i regimen (p = 0.015). Ongoing analysis include identifying predictors of CDK4/6i adherence in these patients using logistic regression analysis.

Conclusion:
Our study showed that 48% of the patients are non-adherent to their CDK 4/6i’s. Patient-centered interventions are urgently needed to improve adherence to CDK4/6i’s in HR+/HER2- BC patients.

References (must also be included in final poster): 1. Cersosimo RJ. Cyclin-dependent kinase 4/6 inhibitors for the management of advanced or metastatic breast cancer in women. Am J Health Syst Pharm. 2019;76(16):1183-1202. doi:10.1093/ajhp/zxz121

2. Johnston SRD, Harbeck N, Hegg R, et al. Abemaciclib combined with endocrine therapy for the adjuvant treatment of HR+, HER2-, node-positive, high-risk, early breast cancer (monarchE). J Clin Oncol. 2020;38(34):3987-3998. doi:10.1200/JCO.20.02514

3. Cristofanilli M, Turner NC, Bondarenko I, et al. Fulvestrant plus palbociclib versus fulvestrant plus placebo for treatment of hormone-receptor-positive, HER2-negative metastatic breast cancer that progressed on previous endocrine therapy (PALOMA-3): final analysis of the multicentre, double-blind, phase 3 randomised controlled trial. The Lancet Oncology. 2016;17(4):425-439. doi:10.1016/S1470-2045(15)00613-0

4. Harbeck N, Rastogi P, Martin M, et al. Adjuvant abemaciclib combined with endocrine therapy for high-risk breast cancer: updated efficacy and Ki-67 analysis from the monoarchE study. Ann Oncol. 2021;32(12):1571-1581.

5. Martin S, Pflumio C, Trensz P, et al. Consequences of Discontinuing a 4/6 Cyclin D-Dependent Kinase Inhibitor During Endocrine Treatment in Hormone-Sensitive Metastatic Breast Cancer Patients in the Context of the COVID-19 Outbreak. Clinical Breast Cancer. 2023;23(1):32-37. doi:10.1016/j.clbc.2022.10.006