Expression of high-molecular-weight cytokeratin is different between UDH and other IPLs: UDH consistently displayed the presence of a population of cytokeratin 5/6-expressing basal-type cells within the proliferative lesion, whereas ADH and LG-DCIS lacked cytokeratin 5/6-positive cells. Here, KRT5 is linked to ductal breast carcinoma in situ.