Real-world study of treatment patterns and outcomes in patients with HR-positive breast cancer after progression on CDK4/6 inhibitors

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is) combined with endocrine therapy are standard of care for metastatic HR-positive, HER2-negative breast cancer (HR+ HER2- mBC). Systemic therapy options after progression on CDK4/6is are poorly defined. A real-world study at MD Anderson Cancer Center (Houston, TX) investigated real-world treatment patterns and outcomes of HR+ HER2- mBC patients after progression on CDK4/6i. Among 1826 patients (99% female; median follow-up 32.4 months), the median age at metastasis diagnosis was 56 years. Following progression on CDK4/6is, 43% received chemotherapy, 38% targeted therapy, 12% endocrine therapy alone, and 7% investigational agents. Nearly half (48%) had visceral progression. Median progression-free survival (PFS) on subsequent therapy was 4.73 months (95% CI 4.40-4.96), with no significant difference by therapy type. CDK4/6i duration of 12 months or longer was independently associated with longer PFS (HR 0.86; p=0.021). The authors conclude that following progression on CDK4/6i, most patients received chemotherapy, but PFS did not differ significantly across treatment types.