In the case of ErbB4, nuclear expression of the intracellular domain of this receptor generated by the proteolytic actions of tumour necrosis factor-α-converting enzyme and γ-secretase following ligand binding promotes ER-driven cell growth [23,52], whilst cytosolic and membrane localisation of ErbB4 has been shown to inhibit growth and promote apoptosis in breast cancer cells [53-55]. The gene discussed is ERBB4; the disease is breast cancer.