Abemaciclib: The First FDA-Approved CDK4/6 Inhibitor for the Adjuvant Treatment of HR+ HER2− Early Breast Cancer

Objective: To review the new indication of cyclin-dependent kinase (CDK4/6) inhibitor abemaciclib for the adjuvant treatment of hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2−), axillary lymph node (LN) positive early breast cancer (EBC) at high risk of recurrence and a Ki-67 ≥20%. Data Sources: A literature search was performed through PubMed, ClinicalTrials.gov, and Food and Drug Administration (FDA) website (February 1, 2018, to December 23, 2021) to identify relevant information. Study Selection and Data Extraction: Human and animal studies related to pharmacology, pharmacokinetics, efficacy, and safety of abemaciclib were identified. Data Synthesis: Addition of abemaciclib to standard of care endocrine therapy (ET) for patients with high-risk clinicopathologic features and Ki-67 ≥20% demonstrated 30% reduction in the risk of developing invasive disease and distant recurrence. At 15.5 months, abemaciclib + ET demonstrated a significant improvement in invasive disease-free survival (IDFS) vs ET alone (hazard ratio [HR], 0.75; 95% confidence interval [CI], 0.60-0.93, P = 0.01). At 27 months, IDFS benefit was maintained (HR, 0.70; 95% CI, 0.59-0.82, P < 0.0001). Diarrhea occurred in more than 80% of patients in the abemaciclib arm. Relevance to Patient Care and Clinical Practice: This review describes the clinical applicability of adjuvant abemaciclib for patients with HR+, HER2− EBC at high risk for recurrence. Conclusion: Adjuvant abemaciclib significantly reduces the risk for early development of invasive disease and distant recurrence in patients with HR+, HER2− node positive EBC. Longer follow-up is needed to determine the impact of adjuvant abemaciclib on late disease recurrence and survival outcomes.