135P Characteristics and dosing patterns of US patients diagnosed with HR+/HER2- early breast cancer initiating abemaciclib at a lower dose than the approved 150mg BID

Abemaciclib in combination with endocrine therapy is approved for adjuvant treatment of adult patients (pts) with HR+/HER2-, node-positive, early breast cancer (EBC) at high risk of recurrence. Anecdotal insights indicate providers may initiate abemaciclib at a lower dose (LD) than the approved 150mg twice daily (BID) to aid tolerability with the aim to increase to the approved dose. This real-world (rw) study describes demographic and clinical characteristics, dosing patterns and incidence of pre-specified adverse events (AEs) in pts with EBC who initiated abemaciclib at a LD. This study used the nationwide Flatiron Health electronic health records-derived de-identified database. Pts initiating abemaciclib Oct 2021-Nov 2022 were included. All results were summarized descriptively. Additional analyses were conducted to compare characteristics of pts initiating <150mg BID vs. 150mg BID. Among 453 pts, 65 initiated abemaciclib at <150mg BID (median follow-up time 7.1 months). Median age was 56 years, 33.8% had stage III disease, 49.2% had ECOG score of 0 and median Charlson comorbidity score was 0. Abemaciclib was frequently combined with aromatase inhibitors (92.3%). The most common starting doses were 100mg BID (56.9%) and 150mg once daily (QD) (24.6%), the time to first dose increase was 71 and 15 days, respectively. At first dose modification, 32.3% pts increased dose to 150mg BID (Table). Common rwAEs were diarrhea (58.5%), fatigue (52.3%), and nausea/vomiting (40.0%). In comparison to pts initiating at 150mg BID (n=388), pts started on a LD were more likely to be aged ≥75 (4.9% vs. 13.8%, p = 0.022). In the rw, pts with HR+/HER2- EBC initiating abemaciclib at < 150mg BID were started on different doses and titration intervals. One-third of pts managed to increase dose to 150mg BID. rwAEs were generally consistent with clinical trial results.Table: 135PDose modification in patients starting abemaciclib <150mg BID by starting dosesOverall cohort (n=65)100mg BID (n=37)150mg QD (n=16)Other dose* (n=12)No dose modification, n (%)28 (43.1)23 (62.2)1 (6.2)4 (33.3)First dose modification, n (%)37 (56.9)14 (37.8)15 (93.8)8 (66.7)Dose decrease761-Dose increase308148Increased to 150mg BID21813-*100mg QD (n=5), 50mg BID (n=6), 50mg QD (n=1) Abbreviations: BID, twice daily; QD, once daily Open table in a new tab