Starting dose of CDK4/6 inhibitors linked to survival in metastatic breast cancer

Progression-free (PFS) and overall survival (OS) are similar between age groups (≥70 and <70 years) among breast cancer patients treated with cyclin-dependent kinase (CDK) 4/6 inhibitors from 2015 to 2019, with no significant differences in neutropaenia or thrombocytopaenia toxicity, reports a study.

However, starting dose shows a significant association with PFS and OS. This finding has not been previously reported, according to the researchers.

In this study, the research team assessed patients with HER2-negative metastatic breast cancer who received CDK4/6 inhibitors from 2015 to 2019 and were stratified according to age ≥70 and <70 years. They also recorded complete blood count from the first two cycles. Haematologic toxicities, dose interruptions and reductions, PFS, and OS rates were then compared between groups.

The researchers explored the haematologic toxicities between the age groups and the association of previous chemotherapy exposure, bone metastasis, and starting CDK4/6 inhibitor dose with PFS and OS.

A total of 202 patients were included, of which 129 were <70 years of age and 73 were ≥70 years. No significant association was found between age group and grade of neutropaenia or thrombocytopaenia. On the other hand, PFS and OS was significantly associated with starting dose. Specifically, patients with recommended starting dose had higher PFS (p=0.0003) and OS (p=0.04) than those with a reduced dose.

“Given the good tolerability across age groups and the improvement in PFS and OS, patients should be treated at the CDK4/6 inhibitors recommended dose and monitored appropriately,” the researchers said.