WT1 and ovarian cancer: Immunohistochemical staining revealed that the secondary M4 ovarian cancer cells isolated from tumors of BALB/c nude mice were similar to the primary M4 ovarian cancer cells isolated from the patient, with no expression of WT1 protein, overexpression and diffuse CA125 protein, complete absence of p53, and a high Ki67 protein proliferation index (60%) (Figure 5).