Real-world experience of chronomodulated prescription of cyclin-dependent kinases 4/6 inhibitor palbociclib in reducing hematological toxicity – A case series

We present six cases of chronomodulated prescription of cyclin-dependent kinases (CDK) 4/6 inhibitor palbociclib and its real-life experience in reducing its hematological side effects. We all know that hematological side effects of palbociclib are to the tune of 70–80% in various clinical trials performed on it. However, with application of chronomodulation, we can reduce this side effect. This will transcend in lesser dose adjustments and may improve the overall survival in adjuvant setup. At present, there is not any overall survival advantage of palbociclib with letrozole in adjuvant setup. Our cases were of metastatic or recurrent hormone-sensitive breast cancer and first 2 were having neutropenia with palbociclib. We decided to chronomodulate and see, to our surprise, there were very few if any neutropenia endured in our observation, all those neutropenia episodes were reversible in the very next cycle, suggestive of some other etiology like viral-induced myelosuppression as the cause. There is not a single episode of persistent grade 2-4 neutropenia even till the writing of this case report.