Adherence to Aromatase Inhibitors ± Abemaciclib Treatment in Patients With Early-stage HER2-negative Breast Cancer

ONCO-ADHER: Adherence to Treatment With Aromatase Inhibitors With or Without Abemaciclib in Patients With Early-stage, Endocrine-dependent, HER2-negative Breast Cancer

Around 90% of breast cancer patients are diagnosed at an early stage and approximately 70% are hormone receptor-positive and HER2-negative (HR+/HER2-). Despite advancements in adjuvant endocrine therapy, 20-30% of early-stage breast cancer patients relapse within the first decade post-surgery. A recent clinically meaningful therapeutic option for these patients has been cyclin-dependent kinases 4/6 inhibitors (CDK4/6 inhibitors). Abemaciclib and ribociclib were assessed in the adjuvant setting, both showing improvement in invasive disease-free survival (IDFS). Abemaciclib has been approved by the FDA and EMA for HR+/HER2- early breast cancer at high risk of disease recurrence and is the first addition to the Slovenian treatment regimen in routine clinical practice.

Poor medication adherence can directly affect the effectiveness of treatment for early HR+/HER2- breast cancer. While adherence data in patients treated with aromatase inhibitors are available, the adherence rate in patients with early HR+/HER2- breast cancer taking abemaciclib remains unclear.

In this study, investigators hypothesize that patients receiving abemaciclib in combination with aromatase inhibitors will have lower medication adherence and higher discontinuation rates compared to those receiving aromatase inhibitors alone. It is expected that patients with better quality of life, better cognitive functioning, and a more positive attitude toward their therapy will demonstrate higher medication adherence rates. Adherence may also be influenced by additional factors, such as age and prior treatments.

Poor medication adherence can directly affect the effectiveness of treatment for early HR+/HER2- breast cancer. While data on medication adherence in patients taking aromatase inhibitors are available, the adherence rate in patients with early HR+/HER2- breast cancer taking abemaciclib remains unclear. Due to the differing characteristics of these treatment modalities, particularly their distinct safety profiles, medication adherence and persistence may vary between them.

It is hypothesized that patients receiving abemaciclib in combination with aromatase inhibitors will have lower medication adherence and higher discontinuation rates compared to those receiving aromatase inhibitors alone. It is also expected that patients with better quality of life, better cognitive functioning, and a more positive attitude toward their therapy will demonstrate higher medication adherence rates. Additionally, factors such as age and prior treatments may contribute to adherence outcomes.

Inclusion Criteria:

• Female,
• Early HR+/HER-2- BC,
• Patient is receiving adjuvant therapy with an aromatase inhibitor (letrozole, anastrozole or exemestane), with or without a CDK4/6 inhibitor abemaciclib, for no more than 18 months,
• Treatment of BC is being conducted at OIL,
• Patient has mandatory health insurance through Health Insurance Institute of Slovenia,
• Patient understands Slovenian language, and
• Patient agrees to participate in the study and provides written informed consent.

Exclusion Criteria:

• Metastatic HR+/HER2-negative breast cancer
• Previous treatment for breast cancer with an aromatase inhibitor, with or without a CDK4/6 inhibitor, for early breast cancer prior to the current adjuvant treatment line