MAPK3 and breast cancer: Previous studies has reported that the misregulated activation of ERK1/2 and c‐MYC promoted the abnormal cell proliferation in various types of cancers, including breast cancer.47, 48 This study showed that the loss of PRKD3 restrained the specific phosphorylation of ERK1(thr202/tyr204), but not ERK2 (Figure 2A and Figure 3A,B).