KRT18 and squamous cell carcinoma: The relationship between CK18 expression and clinico-pathological data could be analyzed in two cancer types derived from CK18 positive precursor cells (breast and kidney cancer), one cancer type derived from epithelium with variable CK18 expression (urinary bladder) as well as in 230 squamous cell carcinomas of various organs of origin (n = 8), but all derived from squamous epithelia that are normally CK18 negative (Table 2, Fig. 4).