Recently the receptor activator of NF-kB (RANK)/RANK ligand (RANKL) pathway was proven to be an important regulator of the mammary stem cell (MaSC) population [3,4] and mammary gland development [5-7], but also, a system with a key role in breast cancer initiation, progression [8,9] and metastasis [10,11]. This evidence concerns the gene TNFSF11 and breast cancer.