ERBB4 and urinary bladder carcinoma: The mRNA expression of two receptors, HER3 and HER4, and four ligands (HRG1–4), including the α and β isoforms of HRG1 and HRG2, was quantified in biopsies from 88 bladder cancer patients (Table 1) and two bladder cancer cell lines (RT4, derived from grade I; and T24, derived from grade III).