Lesions characterized by the presence of columnar epithelial cells lining the terminal duct lobular units (TDLUs) of the breast are being encountered with increasing frequency in breast biopsies performed because of the presence of mammographic microcalcifications. Those lesions in the large majority of the cases are benign. They should be classified into two categories: columnar cell change or columnar cell hyperplasia. Their specific immunophenotype (ER and PR +, Bc12 +) distinguish them from apocrine lesions. Some of them present in addition, cytologic atypia or architectural atypia. When architectural atypia is associated, a careful search for atypical ductal hyperplasia or for low grade DCIS needs to be performed, especially on vacuum assisted macrobiopsies for an appropriate management of the patient.