PCNA and ductal breast carcinoma in situ: We found that the outer myoepithelial layer of the DCIS-like structure was α-SMA positive, and the Mvt-1 cells, which were located inside the ducts and formed DCIS-like structures, were PCNA positive, indicating Mvt-1 cells could form DCIS-like structures within a brief period after injection into the mammary ducts of FVB/N mice via proliferation (Fig 6E and 6F).