Prescribing Patterns and Real-World Clinical Usage of Adjuvant Abemaciclib for Early-Stage, High-Risk, Estrogen Receptor–Positive Breast Cancer

PURPOSE Based on improved invasive disease-free survival in the monarchE trial, the US Food and Drug Administration (FDA) approved abemaciclib for adjuvant treatment of high-risk, estrogen receptor–positive (ER+), human epidermal growth factor receptor 2 (HER2)–negative breast cancer (BC) in combination with endocrine therapy. This study examines real-world prescribing patterns and clinical experiences with adjuvant abemaciclib at an academic cancer center in the United States. METHODS This is a retrospective single-institution cohort study that included patients diagnosed between January 2021 and August 2023 with lymph node–positive, stage II-III ER+/HER2– BC at the University of Pittsburgh Medical Center who would have met eligibility criteria for the monarchE trial. We assessed tumor, provider, and patient factors associated with abemaciclib prescribing using multivariable logistic regression. RESULTS Four hundred sixty-eight patients met monarchE eligibility criteria: 271 (58%) were eligible for abemaciclib under the 2021 FDA approval indications, 324 (69%) met monarchE cohort 1, and 144 (31%) met cohort 2 eligibility criteria only. In the entire cohort, 162 (35%) received a prescription, which was higher in patients meeting FDA approval indications (44%) and lower in those meeting only cohort 2 eligibility (20%). Prescribing increased from 28% in 2021 to 42% in 2022 ( P = .0097). Younger age at diagnosis, higher nodal burden, and higher tumor size were significantly associated with abemaciclib prescribing. Patient refusal was the primary reason for nonprescription (55%). Among those prescribed abemaciclib, 81% experienced toxicities, 47% required dose modifications, and 20% discontinued treatment before completion, primarily due to diarrhea. Abemaciclib prescription was associated with a 66% lower risk of recurrence after adjustment for age, BMI, nodal status, and other variables. CONCLUSION Adjuvant abemaciclib prescribing was low despite its proven benefits. Further research is needed to address prescribing barriers and understand decision-making factors.