The present invention relates to a pharmaceutical composition for preventing and treating cancer, cancer metastasis and bone metabolic diseases, which comprises FSTL1 (Follistatin-like 1) protein as an active ingredient. More specifically, FSTL1 inhibits AKT activity and increases activity of tumor suppressor protein PTEN (phosphatase and tensin homolog deleted on chromosome 10), while inhibiting DNA binding of NF-κB (nuclear factor-κB) and blocking the expression of target genes IL-6, GM -CSF, MMP-9, VEGF and ICAM1, and exhibits significant inhibitory effects on breast cancer growth and metastasis in animal models. Therefore, it can be useful for inhibiting cancer metastasis including breast cancer.
