C3 and primary central nervous system lymphoma: Detailed quantification of these 438 proteins revealed a group of 13 bona fide plasma proteins (serum albumin, serotransferrin, immunoglobulin heavy constant gamma 1, complement C3, hemopexin, alpha-1-antitrypsin, prostaglandin-H2 D-isomerase, apolipoprotein A-I, transthyretin, immunoglobulin heavy constant gamma 2, complement C4-A, beta-Ala-His dipeptidase and alpha-1-acid glycoprotein 1) with concentrations above 1 mg/L, comprising 90% and 86% of the total protein amounts in PCNSL patients and tumor-free patients, respectively (Figure 3A and 3B).