A new study has created the world’s largest and most comprehensive map of normal breast tissue, providing an unprecedented understanding of mammary biology that may help identify therapeutic targets for diseases such as breast cancer. The Human Breast Cell Atlas used single-cell and spatial genomic methods to profile more than 714,000 cells from 126 women. The breast atlas highlights 12 major cell types and 58 biological cell states, and identifies differences based on ethnicity, age and the menopause status of healthy women.