PIM1 and breast cancer: As expected, facilitating PIM1 expression in breast cancer cells (MCF‐7, T47D, MDA‐MB‐231 and BT‐549) led to elevated mammospheres formation capacity and that was reduced by additionally overexpression of RUNX(4A)‐FLAG, which is deficient of the phosphorylation sites targeted by PIM1 (Figure 3A,B).