Key PointsQuestionWhat are the trends and disparities of treatment among women with early breast cancer in China and the US?FindingsIn this cross-sectional study of 57 720 patients with early breast cancer diagnosed from 2011 to 2021, patients in China were younger and had more late-stage and aggressive cancer subtypes. Of these, 69% of patients withERBB2(formerlyHER2orHER2/neu)-positive cancer received trastuzumab-based therapy after 2017 in China compared with 62% of patients in the US during the same period.MeaningThese findings suggest that disparities in early breast cancer treatment between patients in China and patients in the US narrowed gradually from 2011 to 2021.