Adherence to endocrine therapy including ovarian suppression: A large observational cohort study of US women with early breast cancer.

The use of OS among young, commercially insured patients with breast cancer increased over time in agreement with recent clinical trial results but remained relatively low. Nonadherence to ET was common, but the use of OS was not associated with lower adherence to ET in this observational, nonrandomized cohort. These findings may reassure oncologists that use of OS does not endanger ET adherence, although prospective studies are needed for confirmation.