This study investigated phosphoramide mustard-hemoglobin (PAM-Hb, pmol g−1 Hb) as a biomarker of CPA exposure in 135 female breast cancer patients receiving CPA during three courses based on BSA: 500 mg/m2 (C500 group, n = 67) or 600 mg/m2 (C600 group, n = 68). Here, GSTM1 is linked to breast cancer.