The study by Fan et al. [96] identified peptides KNG1K438-R457, derived from kininogen-1 (KNG1), and C3fS1304-R1320, part of complement C3 (C3), as putative peptide candidates for differentiating BRCA1 mutant breast cancer from sporadic breast cancer and cancer-free BRCA1 mutant carriers. Here, C3 is linked to breast cancer.