Although we previously used knockdown approaches to examine the effects of RRAS2 depletion on the growth of human and murine BC cell lines both in vitro and in vivo [47], the derivation of the CBM-MBC21 cell line from a breast tumor that arose in a mouse engineered to overexpress RRAS2 provided a unique opportunity to assess its relevance. This evidence concerns the gene RRAS2 and breast cancer.