NPB and breast cancer: A correlation analysis among the biomarkers showed that the GSACV indexes were obviously positively related to each other (p < 0.001–0.05, respectively) and that the GSACV indexes were significantly negatively correlated with the B6 concentration: r = −0.764, −0.615, −0.563, −0.448, −0.761, and −0.601 for MNBN, NPB, NBUD, MONO, APO and NEC (p < 0.001–0.05), respectively, in the breast cancer cases, and r = −0.582, −0.609, −0.574, −0.411, −0.663, and −0.510 for MNBN, NPB, NBUD, MONO, APO and NEC (p < 0.001–0.05), respectively, in the controls.