# Real-World Toxicity and Effectiveness Study of Abemaciclib in Greek Patients with Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Breast Cancer: A Multi-Institutional Study

## TL;DR

This study confirms abemaciclib is safe and effective for breast cancer patients in real-world settings, with manageable side effects.

## Contribution

Provides real-world evidence of abemaciclib's safety and effectiveness in Greek patients with HR+/HER2- breast cancer.

## Key findings

- Diarrhea was the most common side effect, mostly mild and manageable.
- Two-year disease-free survival was 90.8% for early-stage patients.
- One-year progression-free survival was 78% for advanced cancer patients.

## Abstract

This real-world, multi-institutional study assessed the safety and effectiveness of abemaciclib in combination with endocrine therapy for hormone receptor-positive/HER2-negative breast cancer. Our findings confirm the tolerability and efficacy of abemaciclib in both early and advanced settings, including in older patients. Toxicity was manageable with appropriate interventions, while no new safety concerns were reported.

Background/Objectives: This study aimed to assess real-world toxicity and efficacy data of patients with early and advanced breast cancer (BC) who received treatment with abemaciclib. Methods: This was a prospective/retrospective multi-institutional collection of clinicopathological, toxicity, and outcome data from patients with early or metastatic hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative BC who received treatment with abemaciclib in combination with endocrine therapy in departments of oncology in Greece. Treatment combinations of abemaciclib with any endocrine therapy were accepted. The primary end point was toxicity rate in all patients of the study. Results: From June/2021 to May/2024, 245 women received abemaciclib/endocrine combination therapy; the median age was 57 years. Of these, 169 (69%) received abemaciclib as adjuvant therapy for early-stage disease, while 76 (31%) were treated for advanced BC. At the time of the data cutoff, 133 (84.7%) patients remained in the 2-year treatment period. The most common adverse event (AE) was diarrhea (51%), primarily Grade ≤ 2. Dose modifications due to AEs were required in 19.2% of cases, while treatment discontinuation occurred in 5.1%. There was no difference in dose modification/discontinuation rates between older patients (>65 years) and the remaining patients. For early-stage BC patients, the 2-year DFS and OS rates were 90.8% and 100%, respectively. In patients with advanced cancer (70, 30.8%), 1-year PFS and OS rates were 78% and 96.3%, respectively. Conclusions: This study confirms the safety and effectiveness of abemaciclib in alignment with registrational trials offering valuable insights into toxicity management and clinical outcomes in routine practice without identifying new safety concerns. Clinical Trial Registration: ClinicalTrials.gov NCT04985058.