Salivary markers for breast cancer secondary to HER2/neu status

Objective: The protein c-erbB-2, also known as Her2/neu, is a prognostic breast cancer marker assayed in tissue biopsies from women diagnosed with malignant tumors. Her2/neu overexpression is generally associated with poor patient outcomes. Considering that current methodologies for HER2/neu receptor status are invasive, expensive and often inaccurate, the objective of this study was to compare the salivary protein profiles of pooled saliva specimens from individuals diagnosed with ductal carcinoma of the breast with and without HER2/neu overexpression as a potential alternate to current HER2/neu assessment methodologies. Methods: Pooled (n=10 subjects/pooled specimen) stimulated whole saliva specimens from women were analyzed. One pooled specimen was from healthy women, another was from women diagnosed with Stage IIa (T2N0M0) invasive ductal carcinoma (IDC) without positive HER2/neu receptor status. A third pooled specimen was from women diagnosed with Stage IIa (T2N0M0) IDC with a positive HER2/neu receptor status. Isotopically tagging proteins in the tumor groups and comparing them to the healthy control group measured differential expression of proteins. Experimentally, saliva from each of the pooled samples was trypsinized and the peptide digests labeled with the appropriate iTRAQ reagent. Labeled peptides from each of the digests were combined and analyzed by reverse phase (C18) capillary chromatography on an LC-MS/MS mass spectrometer equipped with an LC-Packings HPLC. Results: The results of the analyses yielded approximately 174 differentially expressed proteins in the saliva specimens. There were 20 proteins unique to HER2/neu positive receptor status and 28 proteins that were unique to HER2/neu negative status. Conclusions: The study suggests that saliva is a fluid suffused with solubilized by-products of oncogenic expression and that these proteins may be differently expressed in the presence of HER2/neu positive receptor status. Potentially these salivary markers may lead to an alternative method for determining HER2/neu positive receptor status.