Fig. 1

Imbalance of estrogen homeostasis in the serum of BC patients. a The concentrations of estrogens, including estrone (E1), estradiol (E2), 16α-hydroxy estrone (16α-OHE1), 2-methoxy estrone (2-MeOE1), 4-methoxy estrone (4-MeOE1), 2-methoxy estradiol (2-MeOE2), 4-methoxy estradiol (4-MeOE2), 2/4-hydroxy estrone (2/4-OHE1), 2-hydroxy estradiol (2-OHE2), and 4-hydroxy estradiol (4-OHE2), in serum samples from NC (49 healthy women, mean age of 43.7 ± 8.80 years) and BC (64 breast cancer patients, mean age of 45.5 ± 5.04 years) were detected by LC-MS/MS. *, p < 0.05, **, p < 0.01 vs control group. The results are shown as mean ± SEM values to depict the levels of estrogens in serum of BC patients and healthy women. b Orthogonal Projections to Latent Structures-Discriminant Analysis (OPLS-DA) score plots of serum (R2X(cum) = 0.335, R2Y(cum) = 0.264, Q2(cum) = 0.003) estrogen metabolites in NC group (green) and BC group (blue) generated by SIMCA 14.0 software. c Variable importance in the projection (VIP) values calculated from OPLS-DA models for estrogen metabolic profile data