Initial real-world experience with ribociclib in advanced breast cancer

PurposeCDK4/6 inhibitors, such as ribociclib, are recommended in combination with hormonal therapy to treat advanced/metastatic hormone receptor-positive, HER2-negative breast cancer. The objectives of this study are to evaluate the therapeutic outcome and tolerance of ribociclib in patients treated at our institution.MethodsThe initial cohort of patients who received >1 cycle of ribociclib between December 2018 and March 2022 were included. Rates of adverse events (AEs) related dose reduction and discontinuation of ribociclib were used as a surrogate marker for intolerance.ResultsSixty-eight female patients were included. Ribociclib was administered with letrozole or fulvestrant in the first-, second-, third-, and fourth-line palliative hormonal therapy settings in 29 (42.6%), 26 (38.2%), 12 (17.6%) and 1 (1.5%) patients respectively. Adverse events (AEs) related dose reduction was reported in 30 (44%) patients. Ribociclib was permanently discontinued in 42/68 (61.8%) patients [Disease progression 33/68 (48.5%) and AEs 9 (13.2%)]. Objective response was documented in 10/61 (16.4%) evaluable patients. The median progression free survival (PFS) was 18 months (95% CI: 11.7-24.3). The median overall survival (OS) was not reached and 84% of patients were alive at 3 years.ConclusionsAlthough objective response rates were modest in this mixed cohort of heavily pretreated patients, ribociclib combined with letrozole or fulvestrant has shown robust PFS and OS in real-world practice. AEs related treatment discontinuation rate is higher than that reported in clinical trials with stringent inclusion criteria.