The molecular weight of cytokeratin 7 (CK7) is 54 kDa, which mainly marks the glandular epithelium and transitional epithelium. The epithelial cells of ovary, lung and breast are CK7 positive, while the epithelial cells of colon, prostate and gastrointestinal tract are CK7 negative. Therefore, CK7 + can be used to distinguish ovarian cancer (CK7 +) from colon cancer (CK7 -).