CPA4 and breast cancer: When the results of the BC group were statistically analyzed based on subgrouping by tumor characteristics, the measured CPA4 mRNA (gene expression) levels showed significant difference, with respect to the molecular subtype (p = 0.006), pN status (p = 0.023), and pathological stage (p = 0.039), while the serum CPA4 measurements differed significantly in terms of pathological type only (p = 0.024) (Table 3).