(009) Analysis of Early Discontinuations, Dose Adjustments, and Adverse Events in Patients with HR+, HER2- Early-Stage Breast Cancer Receiving Adjuvant Abemaciclib with Endocrine Therapy

Poster Abstract:

Background: Hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) early-stage breast cancer (EBC) represents 70% of all breast cancers. These patients are treated with a combination of surgery, radiation therapy, adjuvant/neoadjuvant chemotherapy, and adjuvant endocrine therapy (ET) with aromatase inhibitors or selective estrogen receptor modulators with curative intent. However, 20% of patients with HR+ EBC treated with adjuvant ET will have distant relapse in the first 10 years with the risk of recurrence peaking at 2 years.

Abemaciclib is an oral, cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor that is FDA-approved in combination with ET for adjuvant treatment of adult patients with HR+, HER2-, lymph node-positive, high risk EBC based on the MonarchE study. In MonarchE, 97.9% of patients reported adverse events (AEs) with abemaciclib plus ET with 45.9% reporting Grade ≥ 3 AEs. 68.1% of patients required dose adjustments and 16.6% of patients discontinued abemaciclib prior to 2 years. However, there are no studies describing early treatment discontinuations, dose adjustments, and onset of AEs (except for diarrhea) outside of the ideal, highly controlled clinical trial setting.

Objectives: To describe the rate of and time to early discontinuation and dose adjustment of adjuvant abemaciclib in patients with HR+, HER2- EBC and to describe the incidence and onset of select AEs in the real-world setting. This study’s description of select AEs with adjuvant abemaciclib will assist healthcare providers in understanding the characteristics of and managing AEs in this patient population.

Methods: A multisite, retrospective chart review was conducted for adults diagnosed with HR+, HER2- EBC who received adjuvant abemaciclib with ET between September 1, 2020 to October 6, 2023 at all Mayo Clinic sites. Patients were excluded if they received abemaciclib for metastatic disease, treatment with other CDK4/6 inhibitors adjuvantly, or were receiving an investigational agent for EBC at the same time as adjuvant abemaciclib. The primary endpoint was the incidence of, time to, and reasons for early discontinuation of adjuvant abemaciclib. The secondary endpoints were the incidence of, time to, and reasons for dose adjustments and incidence and onset of select AEs or death due to adverse events.

Results: Data collection is ongoing, and results will be available at time of presentation.

Discussion/

Conclusions: Conclusions will be available after data collection is complete and results are analyzed.

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