PCNA and neoplasm: The highly proliferative nature and mitotic activity of tumor cells in the TGFBR1-CAAcre ovaries were revealed by the presence of mitotic figures (Figure 1H), positive staining of cell proliferation markers Ki67 (Figure 5B) and proliferating cell nuclear antigen (PCNA; Figure 5C), and expression of mitotic marker phospho-histone H3 (pH3; Figure 5D).