Background and importance Therapeutic management of luminal metastatic breast cancer (MBC) has suffered significant progresses with the approval of cyclin-dependent kinase (CDK) inhibitors such as ribociclib.

Aim and objectives To know the characteristics of patients treated with ribociclib as first-line in our centre, and efficacy, frequency and severity of adverse reactions (ARs) associated with it. To compare our results with the pivotal trial MONALEESA-2 of ribociclib as first-line treatment.

Material and methods Retrospective, observational, descriptive study of women aged ≥18 years that received ribociclib as first-line treatment until July 2020 in a tertiary hospital. Follow-up was carried out until March 2021. Following the PFS was cut short by the end of the study.

Variables: age, Eastern Cooperative Oncology Group (ECOG) scale, hormonal therapy in combination, length of treatment, progression-free survival (PFS), ARs, dose adjustment, treatment interruption and suspension.

ARs were classified according to National Institute Cancer: Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Data were collected from patients’ medical records and dispensing software. PFS was calculated by Kaplan–Meier using SPSS software.

Results Fourty patients were included, median age 62 (rank 41–81) years. ECOG before starting: 0 (n=26), 1 (n=13) and 2 (n=1). Ribociclib was used in combination with fulvestrant (n=6), letrozole (n=30), exemestane (n=3) and anastrozole (n=1). Median length of treatment 19 (2–38) cycles. Twenty-four patients continued ribociclib at the end of the study. Sixteen discontinued permanently: twelve due to disease progression, one death and three ARs (liver–kidney toxicity and neutropenia).

PFS were 26.2 months (95% CI 21.9 to 30.5), similar to the pivotal trial, MONALEESA-2 (25.3 months). Initial dose was 600 mg in 37 patients and 400 mg in three patients. Twenty required dose reduction, of which 16 required 400 mg, and four were first reduced to 400 mg and then to 200 mg. Administration was delayed for at least 1 week due to ADRs (n=24).

Twenty presented grade ¾ ADRs: neutropenia (n=9), impaired liver profile (n=6), skin toxicity (n=4), anaemia (n=2); vomiting/diarrhoea, oedema, renal toxicity and asthenia (n=1).

Conclusion and relevance In our centre, ribociclib was used in accordance with indications. Likewise, the pattern of ARs was similar, highlighting neutropenia as dose limiting. As hospital pharmacists is necessary to manage AEs and dose reductions; and improve adherence to obtain the best therapeutic outcomes.

References and/or acknowledgements 1. Hortobagyi GN, Stemmer SM, Burris HA, et al. MONALEESA-2, a phase III trial of first-line ribociclib plus letrozole versus placebo plus letrozole in hormone receptor-positive, HER2-negative advanced breast cancer. Ann Oncol 2018;29(7):1541–1547. doi:10.1093/annonc/mdy155

Conflict of interest No conflict of interest