Breast tissue disorder. Light micrograph of a section through breast tissue displaying apocrine metaplasia. Metaplasia is the abnormal process of tissue changing into another type of tissue. Here, the section has passed through a duct (upper left) to reveal the epithelial (wall surface) cells that line the duct and its lumen (white). The cells are stained pink and the cell nuclei are stained dark purple. The appearance of the cell surfaces has changed, becoming more pitted as they secrete into the lumen. This makes them appear like an apocrine (sweat gland) epithelium. The condition is seen in fibrocystic disease of the breast, and may arise from a hormonal imbalance. Magnification unknown.