ALDH1 expression and distribution over age groups. A. Representative photographs of tissue microarray punches of human breast cancer specimens immunohistochemically stained for ALDH1 with representative examples of no staining (left panel), intermediate staining (middle panel) and strong staining (right panel). Bar represents 100 μm. B. ALDH1 status according to age (N = 496). Logistic regression P-value is shown.