In a murine intratibial osteosarcoma xenograft model, two types of inhibitors were tested: (a) a soluble activin type IIA decoy receptor (ActRIIA‐mFc), or (b) a modified variant of follistatin (FSTΔHBS‐hFc), either alone or in combination with a bisphosphonate. Here, FST is linked to osteosarcoma.