MMP9 and breast cancer: The elevated circulating mRNA and protein levels of PGLYRP1/TAG7, CAMP/LL37, MMP9/collagenase IV and CEACAM8/CD66b before and after the first dose of DOX chemotherapy were associated with increased risk for subclinical cardiotoxicity in breast cancer, and the cut-off values were established as predictors for the adverse course of DOX.