A columnar cell lesion characterized by the presence of enlarged terminal ductal lobular units with dilated acini. The acini are lined by more than two layers of columnar epithelial cells. Prominent apical cytoplasmic snouts are present. Secretions are often present in the lumina of the dilated acini. The disease is columnar cell hyperplasia of the breast (MONDO_0006166). Also known as: CCH, columnar cell hyperplasia of breast.