The effect of switching from ribociclib to palbociclib due to toxicity in hormone receptor-positive, HER2-negative metastatic breast cancer: a real-world, multicenter, retrospective study.

The standards of care for hormone receptor (HR)-positive, HER2-negative metastatic breast cancer are CDK 4/6 (cyclin-dependent kinase) inhibitors. Treatment-related toxicity may develop, leading to a switch between CDK 4/6 inhibitors. This study aimed to investigate the effect of switching from ribociclib to palbociclib on prognosis. Forty-four patients were included in the retrospective, multicenter study. Toxicity causes, Drug-Drug Interactions (DDI), Objective Response Rates (ORR), and Discontinuation Free Survival (DFS) were examined. All patients were female, with a median age of 57 (50.25-67.5). De novo metastatic disease was present in 30 (68.2%) patients, and 33 (75%) patients were postmenopausal. The most common reason for the switch was an increase in alanine aminotransferase in 16 patients (36.3%). The median (m) time to switching was 4.3 months, and the median follow-up period was 23.9 months. There was no statistically significant difference between DDI and switch time, p = 0.118. The ORR was 70.9% in those treated with ribociclib before toxicity and 73.1% after switching. In patients treated with ribociclib in the first line, mDFS1 + DFS2 was 31.6 (23.6-39.6) months in those who switched < 4.3 months (n:18), while in those who switched ≥ 4.3 months (n:16), mDFS1 + DFS2 was 25.5 (20.1-31) months, p = 0.618. Time-dependent Cox regression analysis revealed that the timing of the switch did not affect the prognosis. In HR-positive HER2-negative metastatic breast cancer, no statistically significant negative association was observed in terms of survival and prognosis when switching from ribociclib to palbociclib after toxicity. Switching may be considered in selected patients during the treatment.