ERBB4 and cancer: The ErbB family (ErbB1/EGFR, ErbB2/HER2, ErbB3/HER3 and ErbB4/HER4) of receptor tyrosine kinases (RTKs) is known to drive both formation and progression of a number of commonly occurring cancers, including breast cancer, due to the normal role of these RTKs in regulating cell growth and survival (Yarden and Sliwkowski, 2001; Hynes and Lane, 2005).