Safety and Efficacy of Ribociclib after Palbociclib in Patients with Metastatic Breast Cancer and Intolerable Toxicity

We present in this report two cases of hormone-receptor positive and HER-2/neu negative metastatic breast cancer treated in the first line setting with combination endocrine therapy and palbociclib. Case number one is that of a pre-menopausal woman who received luteinizing hormone-releasing hormone LHRH-analog (goserelin), fulvestrant and palbociclib and developed grade 3 oropharyngeal mucositis requiring interruption, dose reduction and discontinuation of palbociclib. Case number two is that of a post-menopausal woman who developed severe skin rash after treatment with anastrozole and palbociclib in whom the rash disappeared upon stopping palbociclib. Both patients developed intolerable toxicity that ended with discontinuation of palbociclib and were shifted to hormonal therapy plus ribociclib, with which those side effects did not recur. Both patients continued to have a good response to hormonal therapy plus ribociclib. We conclude from our report that cyclin-dependent kinase (CDK) 4/6 inhibitors palbociclib and ribociclib, apart from their known common toxicities such as neutropenia, have different toxicity profiles and can be safely exchanged in case of mucositis or skin rash and remain beneficial.