KIT and breast cancer: Several studies have identified the involvement of putative signaling pathways entailed in the arising of YA-BC, irrespective of the BC subtype, such as growth factor-related pathways (mTOR, MAPK, PI3K/AKT, NF-kB, PTEN) as well as signaling cascades related to mammary stemness and immature cell populations (RANKL and c-kit) [1, 8, 13, 15].