Abstract PS2-04-14: Safety of Ribociclib for patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer: the Royal Marsden experience

Abstract Background: Ribociclib is approved in combination with an aromatase inhibitor (AI) or fulvestrant for patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer, and more recently has been approved as an adjuvant treatment in combination with an AI for patients with HR-positive, HER2-negative early breast cancer at higher risk of recurrence. Therefore, evaluating its safety in a less selected patient population in the real world is key. We aimed to evaluate it in patients treated at our Institution. Methods: We retrospectively identified patients with HR-positive, HER2-negative breast cancer who received Ribociclib between December 2017 and February 2024 at our institution. Demographics, disease characteristics, blood tests and toxicities were recorded for 90 patients. Simple statistics were used as appropriate. Results: Ninety patients were included in the analysis with a median age of 58 years (range: 30-86). Out of these, 27 (24.3%) were 50 years old and 50 (55.6%) were white, 78 (92.9%) had an ECOG performance status of 0-1 and 26 (29.2%) were premenopausal. Thirteen patients (14.4%) were receiving Ribociclib in the adjuvant setting, while 77 (85.5%) with palliative intent. Out of those with advanced disease, 46 patients (59.7%) had visceral metastases and 74 (96.1%) bony metastases. Forty-five (54.2%) had grade 3 tumours. Among patients with complete safety data, 72 (82.8%) had any grade of neutropenia (grade 3-4 in 48 55.2%), thirty-one (36.0%) had any grade of deranged liver function (grade 3-4 in 7 8.1%), 40 (45.5%) had any grade of anaemia, 20 (22.7%) had any grade of nausea, 30 (34.0%) had any grade of fatigue, 13 (14.7%) had any grade of skin rash and 1 (1.1%) had any grade of interstitial lung disease; seven patients (9.1%) had QTc prolongation (grade 1 in all patients). Ribociclib was dose reduced in 35 patients (41.7%) and discontinued in 54 patients (62.8%): due to progression in 33 (61.1%), hepatotoxicity in 4 (7.4%), haematological toxicity in 3 (5.6%) and patient preference in 2 (3.7%). Conclusions: Our analysis of the safety profile of ribociclib in this population confirms a similar neutropenia and dose reduction rate compared with published trials findings. However, rates of anaemia and deranged liver function were higher in our patient population. These findings are key to inform decision-making in a less selected patient population in the real world, especially ahead of the increasing use of ribociclib in the curative setting. Citation Format: A. Pomeranc, N. Chukwuma, E. Crewe, C. Courtney, J. Din, W. Hodgson, R. Binoy, P. Mone, S. Shrestha, R. Smith, S. Butt, A. Chung, O. Cornwall, M. Aboulela, Z. Campbell, S. McGrath, S. Redana, A. Ring, S. Johnston, N. M. Battisti. Safety of Ribociclib for patients with hormone receptor-positive, human epidermal growth factor receptor 2 (HER2)-negative breast cancer: the Royal Marsden experience abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-04-14.