ISG15 and ovarian serous tumor: Immunolocalization of the ISG15 protein in normal fallopian tubes, normal ovarian surface epithelium, borderline ovarian tumors, and low and high grade serous ovarian cancer also showed high levels of ISG15 protein expression only in the epithelial component of the high grade serous ovarian cancer but not in the epithelial and stromal components of the normal fallopian tubes and other serous ovarian tumor samples (Figure 2B,C).