One of the unique characteristics of HER4, in contrast to the other three ErbB members, is that in some tumors HER4’s activation results in inhibition of tumor growth/tumor proliferation/aggressiveness (breast, pancreatic, bladder, and colon) [6,17,90,91], and its presence can be predictive of improved survival and/or favorable clinical-pathological features [3,18,92,93]. This evidence concerns the gene EGFR and neoplasm.