As cells age, they exhibit unpredictable changes individually, but at the organ level, such as in the breast, there are typical patterns of aging. In the breast, different cell types undergo specific changes as they get older, potentially influencing breast cancer initiation. Analyzing genes in aged vs young breast tissue, the authors observed two patterns: genes either changed in a particular direction or became more varied with age. Luminal cells within the breast may act as a canary in the coal mine, as they experience the most changes to gene regulation and variance. Indeed, the luminal aging signature distinguished normal from diseased tissue and was able to predict breast cancer subtypes.