ERBB4 and neoplasm: EGFR is one of four members of the HER/erbB family of receptor tyrosine kinases [HER1 (EGFR/erbB1), HER2 (neu, erbB2), HER3 (erbB3), and HER4 (erbB4)] that is present on all epithelial and stromal cells, and on many smooth muscle cells; however, EGFR overexpression and aberrant EGFR expression has been observed in numerous tumor cell correlates with increased proliferative, angiogenic activity, and poor prognosis [52].