Tao L, et al. - Researchers evaluated data from the population-based California Cancer Registry for 38,509 younger (aged 18–49 years) and 121,573 older (aged ≥ 50 years) women with stage I-III breast cancer (2005–2014) in order to assess the factors associated with age-specific mortality differences. Compared with younger patients, 17% higher disease-specific mortality was evident among older breast cancer patients at diagnosis. They observed higher mortality rate ratios (MRRs) for older vs younger patients with hormone receptor (HR)⁺/HER2^– and HR⁺/HER2⁺, but not for HR^–/HER2⁺ nor triple-negative breast cancers. Higher mortality in older vs younger patients was diminished among patients who received guideline-concordant therapy and reversed among those seen at an NCI-designated cancer center.