Safety and efficacy of ribociclib in combination with letrozole in an extended population of patients with HR+/HER2- advanced breast cancer: analysis of data from a subgroup of patients from Russia in the phase lllb CompLEEment-1 study

Background. The use of cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors in combination with endocrine therapy is a key initial treatment for advanced luminal HER2-negative (HR+/HER2-) breast cancer. The approval studies MONALEESA-2 and 7 demonstrated the efficacy and safety of ribociclib in combination with aromatase inhibitors as a first-line treatment in post- and premenopausal patients. In the Phase lllb CompLEEment-1 study, the same treatment regimen was evaluated in an extended patient population in terms of both safety and efficacy. The article presents an analysis of data from a subgroup of patients from Russia. Materials and methods. The study included 129 patients from Russia who met the inclusion criteria for the CompLEEment-1 study. The primary endpoint was the incidence of adverse events (AEs) at a median follow-up of 25.4 months. Secondary endpoints were median progression-free survival, objective response rate, and disease control. Results. The efficacy and safety results of the therapy in the subgroup of patients from Russia were consistent with the general population of patients included in CompLEEment-1. The incidence of AEs requiring dose adjustment or treatment interruption was 58.1%, and the permanent discontinuation rate was 15.5%. The most frequently reported treatment-related AEs grade 3 or higher were neutropenia and transaminase increased. Conclusion Data obtained in a subgroup of patients from the Russian Federation confirm the safety and tolerability of ribociclib in an extended population of patients with HR+/HER2- breast cancer in settings close to the real world.