RANKL and RANK in sex hormone-induced breast cancer and breast cancer metastasis.

The receptor activator of nuclear factor-κB (RANK) and its ligand RANKL are best known for their essential function in bone remodeling and bone-related pathologies such as osteoporosis and arthritis. In humans, dysregulation of the RANK-RANKL system is the major cause of osteoporosis in postmenopausal women. Furthermore, appropriate RANKL signaling is also required for the formation of a lactating mammary gland. Both RANKL and RANK are expressed by mammary epithelial cells under the control of sex hormones. Recent data also indicate that RANK and RANKL control the preferential metastasis of breast cancer cells to the bone as well as sex hormone-driven primary mammary cancer. Here we critically review these data with special attention on mammary cancer development.