Consistent with this observation, Volkmer et al. (19) and Ho et al. (21) demonstrated that CK14 defined the most primitive/least differentiated basal-type urothelial carcinoma, which preceded the emergence of cancer cells expressing CK5 (intermediately differentiated) or CK20 (well-differentiated); further, CK14 expression marked the highly tumorigenic stem cell population. The gene discussed is KRT5; the disease is urothelial carcinoma.