We hypothesize that peripheral blood levels of the neutrophil granular proteins peptidoglycan recognition protein 1 (PGLYRP1), cathelicidin antimicrobial peptide (CAMP), matrix metallopeptidase 9 (MMP9), and carcinoembryonic antigen-related cell adhesion molecule 8 (CEACAM8) are associated with a risk of DOX-induced cardiotoxicity in breast cancer patients. The gene discussed is MMP9; the disease is breast carcinoma.