Retrospective analysis of real-world outcomes with first- vs second-line CDK4/6 inhibitors for HR-positive, HER2-negative metastatic breast cancer

A retrospective analysis of a USA-wide database investigated real-world outcomes with first-line endocrine therapy (ET) plus CDK4/6 inhibitor versus first-line ET alone followed by second-line ET plus CDK4/6 inhibitor among patients with HR-positive, HER2-negative metastatic breast cancer (HR+ HER- mBC). The analysis included 2771 patients (2170 first-line CDK4/6 inhibitor and 601 second-line CDK4/6 inhibitor). Patients receiving first-line CDK4/6 inhibitor were younger (75% versus 68% < 75 year old (p=0.0001), less likely uninsured or not having insurance status documented (10% versus 13%; p=0.04), of better performance status (50% versus 43% with ECOG PS 0; p=0.03), and more likely to have de novo mBC (36% versus 24%; p<0.001). Time to third-line therapy (49 versus 22 months; p<0.001) and time to chemotherapy (68 versus 41 months; p<0.001) were longer in those receiving first-line CDK4/6 inhibitor. Overall survival (54 versus 49 months (p=0.33) was similar between groups. The authors conclude that use of CDK4/6 inhibitor with first- versus second-line ET was associated with longer time to receipt of thrid-line therapy and longer time to receipt of chemotherapy.