Abstract P1-17-08: Abemaciclib and endocrine therapy for hormone receptor-positive, HER2-negative advanced breast cancer: A real-world UK multicentre experience

Abstract Background Abemaciclib is approved in 1st and 2nd line for hormone receptor (HR)-positive HER2-negative advanced breast cancer (ABC). However, outcomes on this agent are unclear in the real world.We determined the safety and efficacy profile of abemaciclib across 15 institutions in the United Kingdom. Methods We retrospectively identified HR-positive, HER2-negative ABC patients who received abemaciclib between July 2018 and June 2020. Demographics, disease characteristics, prior treatments, blood tests, toxicities, treatment delays and responses were recorded. Simple statistics, Fisher’s exact test, chi-squared method and Cox regression were used as appropriate. Results 228 patients identified had median age of 64 (31-93). 172 (75.4%) were postmenopausal and 209 (91.7%) had ECOG Performance Status 0-1. 145 (63.6%) had visceral involvement and 44 (19.3%) only bone disease. Patients received a median 1 (range 0-7) prior lines of treatment and 0 (range 0-5) prior chemotherapy lines.148 patients (64.9%) experienced diarrhoea (grade ≥3 in 16 [7.0%]). 146 patients (64.0%) developed neutropenia (grade ≥3 in 40 [17.5%]). 5 experienced febrile neutropenia (2.2%). 32 patients (14.0%) required hospitalisation due to toxicity (diarrhoea in 9 [3.95%]).Dose reductions were required in 107 patients (46.9%), mainly due to diarrhoea (55 [24.1%]) and to 50mg BD in 30 patients (13.2%). Dose delays were in median 14 (range 2-118). Abemaciclib was discontinued in 121 patients (53.1%) due to disease progression in 61 (26.7%) and toxicity in 48 (21.0%) (diarrhoea in 16 [7.0%]).Abemaciclib produced clinical benefit rate of 82.8% and overall response rate of 47.2% in 163 patients assessed. Overall, median progression-free survival (PFS) was 6.4 months (95% confidence interval [CI] 4.4-7.8) and median overall survival (OS) was 8.8 months (95% CI 7.6-10.6). Conclusions This a large real-world analysis of the safety and efficacy of abemaciclib in combination with endocrine therapy for advanced HR-positive breast cancer. In this analysis, the rates of diarrhoea were lower compared with the pivotal trial data, while neutropenia was more frequent. Although the PFS outcomes were similar to those previously reported, median OS was worse in this cohort which may reflect the different population of patients included, who were older and had more frequent visceral involvement. The selection of patients suitable for abemaciclib is crucial to ensure adequate efficacy and safety outcomes in this setting. Citation Format: Nicolò Matteo Luca Battisti, Laura Morrison, Tamsin Nash, Nishanti Senthivel, Samantha Kestenbaum, Parvin Begum, Mariam Obeid, William Hayhurst, Dorothy Yang, Shafiah Gafoor, Caroline Brown, Farah Rehman, Laura Kenny, Olivia Hatcher, Susan Susan, Jennet Williams, Anna Brown, Hamoun Rozati, Alexandros Alexandros, Elinor Sawyer, Charalampos Gousis, Eleni Karapanagiotou, Anna Rigg, Kleopatra Rapti, Rebecca Roylance, Mark Beresford, Abigail L Gee, Apostolos Konstantis, Judy King, Mark Nathan, Emma Spurrell, Mark Pearce, Dane Bradwell, Arshi Denton, Kate Swain, Sophie McGrath, Mark Allen, Alistair Ring, Stephen Johnston, Fharat Raja. Abemaciclib and endocrine therapy for hormone receptor-positive, HER2-negative advanced breast cancer: A real-world UK multicentre experience [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-17-08.