Background and Importance Ribociclib is a selective cyclin-dependent kinase 4/6 (CDK4/6) inhibitor approved for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2−) locally advanced or metastatic breast cancer (LA/MBC) in combination with an aromatase inhibitor or fulvestrant as initial hormonal treatment. Multiple adverse effects were advertised in clinical trials which led to modifications such as dose reductions or drug change.

Aim and Objectives The aim of this study was to evaluate the side effects due to ribociclib and to analyse how modifications in treatments are made in clinical practice.

Material and Methods We conducted a descriptive, observational and retrospective study of patients treated with Ribociclib from 2017 to present in a third-level hospital. The data were obtained from the electronic medical records of the patients and the Farmatools Management program. The parameters analysed were: demographic information, time from first dose to first event noticed (dose reduction/drug change), doses reductions, changes to other CDK4/6 inhibitor, frecuency and description of adverse effects and discontinuation treatment. Data were processed by Microsoft Excel software.

Results A total of 81 women with HR+/HER2− MBC were studied. Median age was 62 years. 62% (50/81) had to undergo some modification with respect the original treatment due to adverse effects. 40% (32/81) required some dose reduction [35% (28/81) only one reduction; 5% (4/81) needed two reductions]. 22% (18/81) had to switch drug. Main signs involved were hematological toxicity -neutropenia- (24 cases), dermal toxicity (8), liver toxicity (5), gastrointestinal toxicity (3), heart toxicity -long QT syndrome- (2). Average time to first dose reduction was 83 days. Average time to drug change was 117 days. Average cycles until first event was 2,5. Average cycles until end of study or event was 6,9. To the end of study, 64% (32/50) continue treatment with ribociclib, 26% (13/50) changed to other cycline inhibitor and 10% (5/50) changed to another drugs. Rest of them was suspended by cancer progression.

Conclusion and Relevance The frequency of dose reductions and interruptions of treatment in our population was similar to clinical trials (MONALEESA). The kind of adverse effects observed was similar too, although we focused on those which supposed dose reduction or drug change.

Conflict of Interest No conflict of interest.