A Comparative Species Framework to Identify Candidate Salivary miRNAs Associated with Breast Cancer Risk

Accurate assessment of early indicators of breast cancer (BC) is critical to improve detection strategies and patient prognosis. Our research group takes a comparative species approach to study early BC detection by capitalizing on data from species with inherently low or high incidence of mammary cancer to supplement rare human samples. Circulating microRNAs (c-miRNAs) are a promising class of molecules that have the potential to serve as biomarkers for BC risk and disease detection. The expression of these non-coding RNAs controls numerous cellular processes and their dysregulation is associated with various pathological conditions, including cancer. To explore whether c-miRNA expression profiles can identify individuals with early-stage BC, we conducted a multi-species pilot study. We analyzed biofluid samples (i.e., saliva, serum, and plasma) from patients with early-stage BC and patients with no prior history of cancer and mammosphere-derived epithelial cells (MDECs) from dogs (canines) and horses (equines), species with a relatively high and low incidence of mammary cancer, respectively. We identified 16 candidate c-miRNAs that were upregulated in saliva from patients in the early-stage BC group when compared to the control patient group. Notably, 6 of these c-miRNAs (i.e., miR-361, miR-148b, miR-205, miR-186, miR-223, and miR-197) were also found to be secreted at higher levels by canine MDECs when compared to equine MDECs. Although individual and combinatorial assessment of these six c-miRNAs in a larger human cohort did not confirm their potential association with early breast cancer detection, the data in this study do introduce a novel comparative framework in which species-to-species variation in cancer susceptibility may inform the identification of candidate biomarkers for human disease.