SPON2 and breast cancer: Using an engineered metastatic niche, we identified a 9‐gene signature (Dhx9, Dusp12, Fhl1, Ifitm1, Ndufs1, Pja2, Slc1a3, Soga1, Spon2) that successfully delineated metastatic breast cancer from nonmetastatic breast cancers including an invasive cell line without metastatic potential.