ATYPIA In biopsy: atypical condition. The breasts are composed of lobes, which produce milk, and ducts, which carry milk to the nipple. The lobes and ducts are lined by two layers of cells. When the cells lining the lobes or ducts grow, the set of cells is called hyperplasia. Habitual hyperplasia is not risky in itself, but when the cells grow in an irregular pattern they can be a sign that the person may develop cancer at some point in their life. This irregular pattern is known as atypia.
