The fact that the EGFR/ERBB2 and ERBB3 expression ratio readily identified two distinct classes of urothelial carcinomas strongly associated with the independently determined molecular subtypes shows that the status of the EGFR, ERBB2, and ERBB3 receptors may represent fundamentally different tumor cell phenotypes (Figure 6). The gene discussed is ERBB2; the disease is urothelial carcinoma.