Background and Importance Ribociclib is a cyclin-dependent kinase inhibitor used in the first line of luminal metastatic breast cancer (MBC).

Aim and Objectives To assess the effectiveness and safety of ribociclib in first-line treatment of hormone receptor positive and human epidermal growth factor receptor 2 (HER2) negative MBC.

Comparison with the results of the MONALEESA-2 trial.

Material and Methods Observational, retrospective study, carried out in a second level hospital between July 2017 and March 2022. All patients diagnosed with MBC treated with ribociclib in combination with hormonal therapy from diagnosis of the first metastasis to tumour progression were included.

The effectiveness variable measured was the median progression-free survival (mPFS).

The safety variables measured were adverse reactions (AR) presented and percentage of patients who required dose reduction due to adverse reactions.

Variables such as gender, age and location of metastases were also recorded.

The data was obtained from the Electronic Medical Record and the Pharmacy dispensing programme.

For analysis of mPFS, the Kaplan-Meier test was used using the statistical program SPSS^® and results were compared with the results of MONALEESA-2 study.

Safety was assessed according to CTCAE criteria.

Results 34 patients were included, 100% were women with a median age of 58 years (31–73).

Locations of metastases found were bone, lung, mediastinum, liver, pleura, skin, brain, and peritoneum. 58.82% (20/34) of patients had 2 or more metastatic locations and 41.17% (14/34) had a single metastasis, this being bone location in 64.28% (9/34) of patients.

The median follow-up was 13.9 months (2.73–29.5), 41.17% (14/34) of patients progressed to treatment with ribociclib and mPFS was not reached.

In MONALEESA-2 study, median follow-up was 26.4 months and mPFS was 25.3 months.

The adverse reactions presented mainly were neutropenia in 52.94% (18/34) and asthenia in 26.47% (9/34). In MONALEESA-2 study, both were adverse reactions reported with a frequency > 20%.

55.88% (19/34) of patients required dose reduction due to adverse effects of ribociclib. In MOONALEESA-2 study, dose reduction was required in 50.6% (10/19) of patients.

Conclusion and Relevance A longer follow-up time is necessary for our patients to be able to compare the effectiveness in terms of PFS with the MONALEESA-2 study. Regarding the safety of ribociclib, the data reflected are similar to those presented in the MONALEESA-2 study.

Conflict of Interest No conflict of interest