Knockdown of PTK6 decreases proliferation in breast cancer cell lines (Harvey and Crompton, 2003) and blocks activity of a GTPase, of ERK5 (extracellular signal-regulated kinase) and p38 mitogen-activated protein kinase (MAPK), but not Akt (Mitchell et al, 1994; Barker et al, 1997; Llor et al, 1999; Born et al, 2005; Ostrander et al, 2007). This evidence concerns the gene PTK6 and breast cancer.