e12529 Background: Abemaciclib in combination with adjuvant endocrine therapy (ET) improves invasive disease-free survival (IDFS) and is standard of care for patients (pts) with high-risk hormone receptor–positive (HR+), HER2-negative early breast cancer (EBC) based on the monarchE trial. Given the prolonged two-year treatment course, evaluation of real-world tolerability provides insight into its use in clinical practice. We examined toxicities and treatment patterns among patients treated with adjuvant abemaciclib. Methods: We conducted a retrospective single-institution analysis, after IRB approval, of pts with HR+/HER2− EBC treated with adjuvant abemaciclib between 2021 and 2024. Demographic, clinical, pathologic, treatment, and toxicity data were abstracted from the electronic medical record. Outcomes were summarized using descriptive statistics. Results: Thirty-nine pts were included in the analysis. Pts were all female, with a median age of 52.9 years (IQR 45.9–62.3). Most pts were White and non-Hispanic (97%), and 62% were postmenopausal. All tumors were ER-positive/HER2-negative; 15% had progesterone receptor expression < 1%. Pathologic stage was III in 51% and II in 49%. All pts received adjuvant ET with aromatase inhibitors; ovarian suppression was used in 26%. Germline BRCA1/2 mutations were identified in two pts. Most pts received adjuvant chemotherapy (85%), with no neoadjuvant chemotherapy use. Eligibility for adjuvant abemaciclib was based on ≥4 positive lymph nodes in 44% of pts and 1–3 positive nodes with additional high-risk features in 56% (including grade 3 disease in 26%, Ki-67 ≥20% in 20%, and/or tumor size ≥5 cm in 10%). Most pts initiated abemaciclib at 150 mg twice daily (92%), with a median treatment duration of 24 months (IQR 18–24). Adverse events (AEs) of any grade occurred in 64% of pts (vs 98% in monarchE). Dose reductions and toxicity-related discontinuation occurred in 56% and 24% of pts, respectively (vs ~48% and 16.6% in monarchE). The most common AE was diarrhea (38% vs 82% in monarchE), followed by fatigue (18% vs 39%), abdominal pain (10%), nausea (10%), and vomiting (8%). Acute kidney injury occurred in 10% of pts and alopecia in 5%, with one thrombotic event observed. No neutropenia was reported (vs 45% in monarchE). Median follow-up was 39.4 months; all pts were alive at last follow-up, with one local recurrence, precluding meaningful IDFS and OS analyses. Conclusions: In this real-world cohort, adjuvant abemaciclib was associated with higher rates of dose modifications and treatment discontinuation compared to rates reported in the monarchE trial. Adverse events were consistent with prior reports, with lower rates of common toxicities and no observed neutropenia. These findings underscore the challenges of maintaining a two-year treatment course in routine practice. Longer follow-up and larger cohorts are needed to better characterize recurrence and survival outcomes.
Haji et al. (Thu,) studied this question.