RSPO2 and breast carcinoma: The molecular mechanism is that R-spondin 2 (RSPO2) and RANKL activate the Gαq/β-catenin signaling pathway by binding to the receptor LGR4, which regulates the expression of DKK1, which binds to LRP5 on osteoclast precursor cells to stimulate the secretion of Rnasek, a chemokine, and promotes bone metastasis of breast cancer (69).