Comparison of breast cancer protein biomarker patterns in serum versus cell-free saliva

Background:
Biomarkers (BM) are measurable biochemical or molecular parameters, which can constitute an indicator for a biologically pathological process. Especially circulating biomarkers derived from body fluids like blood or serum have great potential, however each sample withdrawal holds potential risks like e.g. danger of infection. Therefore, biomarker analysis in saliva could be a potential simple, safe and non-invasive alternative for the future.
To gain deeper insight into the potential of saliva-derived biomarkers and their comparability with BM derived from serum we investigated protein biomarkers as well as tumor-specific autoantibody profiles of saliva and corresponding serum samples obtained from the same individual. For this purpose, we collected in cooperation with the Medical University of Vienna serum and saliva samples of breast cancer patients and healthy control probands.
Methods:
We analyzed and compared tumor-autoantibody profiles of breast cancer- and control proband- derived serum and saliva samples using a targeted breast cancer protein array comprising around 700 previously selected classifier antigens. Furthermore, we also performed a comparative expression analysis of 92 putative cancer-related proteins by using an Olink high-multiplex immunoassay (“Target 96 Oncology1” panel).
Results:
Class prediction analysis of tumor autoantibody screening data identified classifier able to discriminate breast cancer from controls with an area under the curve of 0.856 in serum (199 markers) as well as 0.992 in saliva (133 markers). 87 markers out of both sets overlap. Furthermore, Olink protein marker screening resulted in a 10-marker-classifier in saliva (AUC=0.719) as well as 22- marker-classifier in serum (AUC=0.864), able to discriminate breast cancer from control patient samples.
Conclusions:
We could successfully demonstrate the feasibility to perform protein tumor marker screenings via Olink assays in both serum and saliva samples. Quite comparable autoantibody profiles in serum and saliva further underline the high potential of saliva-derived protein-based biomarkers.