The volcano plots revealed that a total of 123 serum metabolites were changed in the PDC group compared with those in the BC group, of which 70 metabolites were significantly upregulated and 53 metabolites were significantly downregulated (screening criteria were p < 0.05 and variable importance in projection (VIP) > 1.0) (Supplementary Fig. S4). The gene discussed is PDC; the disease is breast cancer.