MAPK1 and neoplasm: Besides their increased tumorigenic potential, ERK2 cells had a higher incidence of tumor initiation: 66% (4 out of 6 injections) of HCT116 ERK2 transplantations resulted in detectable tumors, whereas 50% (3 out of 6 injections) of HCT116 ERK1 cells, 33% (2 out of 6 injections) of HCT116 ERK1/2 cells transplantations, and 33% (2 out of 6 injections) of HCT116 GFP cells yielded tumors (Figure 5h).