Combination treatment with a CDK4/6 inhibitor and aromatase inhibitor (AI) results in similar progression-free survival (PFS) rates in women with hormone receptor-positive, HER2-negative metastatic breast cancer who are aged 70 or older compared to younger women, according to study findings published in the Journal of Clinical Oncology.

Researchers looked at pooled data from the PALOMA-2, MONA­LEESA-2, and MONARCH-3 clinical trials that represented 1,105 patients, 155 of whom were aged 70–74 and 125 aged 75 or older. Those age groups had been previously underrepresented in breast cancer clinical trials, and data on which to base clinical recommendations have been limited.

Overall across all ages, the median PFS was 14.8 months for those receiving an AI alone (i.e., letrozole or anastrozole) and 27.7 months for those receiving an AI plus CDK4/6 inhibitor (i.e., palbociclib, ribociclib, or abemaciclib). Among women aged 75 and older, PFS was 13.7 months with AIs alone and 31.1 months when AIs and CDK4/6 inhibitors were combined.

Older patients were more likely to experience grade 3 or 4 toxicities, particularly diarrhea, fatigue, neutropenia, and increased creatinine. They were also more likely to require dose reductions or interruptions in cycles 1–3 or treatment discontinuation because of adverse events.