The present invention relates to a pharmaceutical composition for preventing and treating cancer, cancer metastasis or metabolic bone diseases, containing follistatin-like 1 (FSTL1) protein as an active ingredient. Particularly, FSTL1, an activator protein 1 (AP-1) target gene, inhibits AKT activity, increases the activity of phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a tumor suppressor protein, blocks the DNA binding of nuclear factor-κB (NF-κB) and the expression of the target genes of IL-6, GM-CSF, MMP-9, VEGF and ICAM1, and exhibits significant inhibitory effects on the growth and metastasis of breast cancer in an animal model, and thus can be useful in inhibiting the metastasis of cancers including breast cancer.
