Background and Importance Ribociclib and abemaciclib are cyclin-dependent kinase 4/6 inhibitors (CDK4/6-i) used as treatment for patients with negative epidermal growth factor receptor 2 (HER2-) and positive hormone receptor (HR+) metastatic breast cancer (MBC). MONALEESA-2 and MONARCH-3 trials evaluated the efficacy of this drugs as first line treatment in post-menopausal women.

Aim and Objectives To assess effectiveness of ribociclib and abemaciclib in HER2- and HR+ MBC in clinical practice, comparing results with reference bibliography.

Material and Methods Descriptive retrospective study included post-menopausal women with HER2- and HR+ MBC receiving CDK4/6-i as first line of treatment between August-2017 and September-2022. Data were recorded from electronic clinical history and prescription program Prisma®: gender, age, ECOG, CDK4/6-i and combined endocrine therapy, dosage and treatment duration. Effectiveness was assessed by progression free survival (PFS), overall survival (OS) and PFS rate at 12 months, using Kaplan-Meyer statistical analysis with SPSS V.21.0. Results were compared with those described in pivotal clinical trials.

Results A total of 63 women were included. Mean age was 63 (range 50–84) years. At baseline, ECOG=0/1 was observed in 93.7% cases and ECOG=2/3 in 6.3%. Abemaciclib was used in 50.8% patients and 49.2% ribociclib. CDK4/6-i were combined with letrozole in 58.7% patients and fulvestrant in 41.3%. Dose reduction occurred in 48.4% patients with ribociclib and 34.4% with abemaciclib. For ribociclib, median treatment duration was 16 (2–54) months and 11 (2–32) months for abemaciclib. Estimated PFS median for ribociclib was 28.0 (95% Confidence Interval: 6.6–49.3) months and was not reached for abemaciclib. Ribociclib and abemaciclib estimated OS median were not reached at data cut-off. PFS rate at 12 months was 67.3% (95% CI: 58.8–75.8) for ribociclib, and 60.7% (95% CI: 51.4–70.0) for abemaciclib. For ribociclib, MONALEESA-2 trial presented a PFS median of 25.3 months, OS median of 63.9 months and 12-month PFS rate of 72.8%. For abemaciclib, MONARCH-3 showed a PFS median of 28.2 months, OS median was not reached and 12-month PFS rate was not described.

Conclusion and Relevance Real-life effectiveness results confirmed a substantial benefit of ribociclib and abemaciclib. These data appeared to be slightly superior than those described in the literature. Larger sample size and longer follow-up time are necessary to extract more conclusive information.

Conflict of Interest No conflict of interest