CD19 and breast cancer: To evaluate the differences in the protein expression in the CD19+ lymphocytes, we used label-free quantification based on ion intensity with stringent criteria: a fold change ≥2 of protein abundance in individual BC groups in comparison to the protein abundance in the control group, a false discovery rate (FDR) ≤ 0.05, high confidence, a minimum of two unique peptides, and correction of the probability score using the Benjamini–Hochberg method.