MAP3K14 and cancer: Figure 4F shows that NIK overexpression increased the size and number of colonies formed by MCF7-NIK+ cells, when compared with MCF7-Mock+ cells. We also found that NIK-overexpressing MCF7 cancer cells developed a higher number of mammospheres and the sphere-forming potential is sustained even after a second passage (Fig. 4G). To further support these results, we evaluated the ability of SKBR3-NIK+ cells to form mammospheres, Supplementary Fig. 3C shows that NIK-overexpressing cells form a higher number of mammospheres than control cells.