Molecular genetic evidence supports the existence of two distinct pathogenetic pathways for bladder cancer development: low-grade papillary superficial tumors (characterized by activation of the receptor tyrosine kinase-Ras pathway, and activating mutations in the HRAS and fibroblast growth factor receptor 3 (FGFR3) genes) and high-grade invasive BC (characterized by alterations in the p53 and retinoblastoma (RB1) pathways). The gene discussed is FGFR3; the disease is urinary bladder cancer.