Mature mammary epithelial cells engineered to express SOX11 showed alterations in progenitor cell populations, including an expanded basal‐like population with increased aldehyde dehydrogenase (ALDH) activity, and increased mammosphere‐forming capacity.DCIS.com cells engineered to express SOX11 showed increased ALDH activity, which is a feature of cancer stem cells. Here, SOX11 is linked to cancer.