5PSQ-161 Effectiveness and safety of palbociclib and ribociclib

Background and importanceSeveral trials have demonstrated the benefit of anti-CDK4/6 inhibitors plus endocrine therapy in oestrogen receptor positive (ER+) advanced breast cancer (aBC), in first or subsequent lines of therapy. Based on clinical trials, palbociclib and ribociclib are equally effective in either firstline or secondline therapy for advanced ER+ aBC, however, different toxicity profiles have been reported.Aim and objectivesTo assess progression free survival (PFS) and safety of palbociclib and ribociclib in real clinical practice.Material and methodsAn observational, retrospective, descriptive study was conducted in patients with aBC treated with palbociclib and ribociclib between February 2018 and September 2020. Age, doses, adverse events, time to progression or death, and medical history were collected.Results42 patients were included (24 received palbociclib and 18 received ribociclib). Ribociclib: mean age at the start of treatment was 58.94±11.79 years. 16.67% of patients withdrew their treatment due to toxicity. 16.67% progressed (PFS of 9.9±5.07 months). Patients began with doses of 600 mg: almost 40% of patients had to reduce the dose, of whom 28.57% had to reduce it to the minimum dose of 200 mg and the rest maintained on the 400 mg dose.Palbociclibmean age at the start of treatment was 59.37±10.74 years. There were only two cases of toxicity (8.33%). 45.83% of patients progressed (PFS of 7.81±6.26 months). Patients started with a dose of 125 mg: 58.33% of patients had to reduce the dose, of whom 28.57% had to reduce to the minimum dose of 75 mg while the rest remained on the 125 mg dose. The main cause of dose reduction for both was neutropenia (50% for ribociclib and 72.22% for palbociclib). The next cause was liver toxicity (37.55%) from ribociclib and gastrointestinal upset (16.67%) from palbociclib.Conclusion and relevanceComparing effectiveness, a greater PFS was found for ribociclib compared with palbociclib (2.09 months); there was a higher percentage of patients with progression after treatment with palbociclib (45.83% vs 16.67%). Regarding toxicity, ribociclib had a higher toxicity profile than palbociclib. Both required dose adjustment, greater for palbociclib, the main cause in both being neutropenia.References and/or acknowledgementsConflict of interestNo conflict of interest