FOS and breast cancer: In this study, we have demonstrated that (i) CSBTA relieved CIBP induced by Walker 256 cells; (ii) prevention of osteolytic bone resorption by CSBTA in vivo was accompanied by suppression of tibia RANKL level; (iii) CSBTA treatment decreased the mRNA levels of Rankl and osteoclast differentiation related cytokine in the mammary tumor cells; (iv) CSBTA decreased RANKL expression and secretion in breast cancer cells; (v) CSBTA could inhibit osteoclastogenesis by suppressing RANKL-induced nuclear factor-κB and c-Fos/NFATc1 pathways.