Volkmer et al. identified three bladder tumor cell differentiation states (basal, intermediate and differentiated) based on the expression of keratins 14, 5 and 20, which are associated with the expression of cell surface markers CD90, CD44 and CD49f: basal or triple positive (CD90+/CD44+/CD49f+), intermediate or double positive (CD90−/CD44+/CD49f+), differentiated or single positive (CD90−/CD44−/CD49f+) and fully differentiated or triple negative cells (CD90−/CD44−/CD49f−). Here, CD44 is linked to urinary bladder neoplasm.