MAP3K21 and breast cancer: In order to evaluate the expression of MLK4 in breast cancer patients we analyzed 818 samples available in TCGA, which showed gene amplification and mRNA upregulation of MLK4 (MAP3K21) in invasive breast carcinoma at a frequency of 23%, in contrast to lower frequency of alterations (6–7%) in the rest of the MLK family members (Fig. 1a and Supplementary Fig. 1a) [17–19].