Serological Proteome Analysis (SERPA) Reveals Breast Cancer-Associated Autoantibodies Targeting Placental Antigens

Background The association between placental development and cancer formation was first proposed over a hundred years ago. In our current investigation, we pioneered the application of serological proteome analysis (SERPA) of human placental proteins to detect tumor-associated antigens that trigger autoimmune responses in breast cancer patients. Methods We employed SERPA to examine serum reactivity against first-trimester placental (FTP) proteins in 86 early-stage breast cancer (BrC) patients and 86 non-cancer controls (non-BrC). Following initial screening, we isolated and characterized differentially reactive proteins using LC-MS tandem mass spectrometry. From these, we unambiguously identified 12 placental proteins showing the most pronounced differential expression between patient and control groups. These candidate biomarkers underwent rigorous validation through both ELISA and immunohistochemical (IHC) analyses. Results Our SERPA screening revealed thirty-three placental proteins exhibiting differential immunoreactivity with breast cancer-associated autoantibodies. Subsequent validation of twelve candidates identified six proteins including PDIA3 (p = 0.0059), STIP1 (p = 0.027), CCT2 (p = 0.0025), PARK7 (p = 0.0002), PRDX6 (p = 0.016) and LDHB (p = 0.0083) that showed statistically significant elevated reactivity with BrC patient sera. Gene Ontology analysis demonstrated that these autoantibody-targeted placental proteins primarily participate in immune regulation and cellular stress response pathways. Immunohistochemistry (IHC) staining of placenta using antibodies directed against PARK7 and PRDX6 recombinant proteins (cloned from FTP), localized their expression predominantly to placental cytotrophoblasts. Notably, in IHC staining of breast cancer and normal breast tissues, PARK7 and PRDX6 exhibited distinct subcellular localization patterns, significantly stronger nuclear staining in normal tissues (p < 0.001) versus predominant cytoplasmic localization in malignant specimens (p < 0.0001). Serum immunoreactivity from BrC patients displayed remarkable specificity, targeting nuclear and cytoplasmic compartments of rare cytotrophoblast subpopulations and syncytial nuclear aggregates. Through combinatorial analysis of placental-reactive autoantibodies, we identified a set of promising biomarker panels with specificity and sensitivity ranging from 64–73% and 77–97%, respectively, demonstrating potential for non-invasive breast cancer detection. Conclusion To the best of our knowledge, this study is the first to propose the use of placental proteins for early breast cancer screening. Our findings establish a novel approach for breast cancer detection and identify potential targets for immunotherapy. However, further refinement and clinical adaptation are needed before translation into diagnostic or therapeutic applications.