Abstract
BACKGROUND: Differentiating benign from canine malignant mammary tumors requires invasive surgical biopsy. Circulating microRNAs (miRNA) may represent promising minimally invasive cancer biomarkers in people and animals. OBJECTIVES: To evaluate the serum mRNA profile between dogs with and without mammary carcinoma, and to determine if any of these markers have prognostic significance. ANIMALS: Ten healthy client-owned female dogs (5 intact, 5 spayed) and 10 dogs with histologically confirmed mammary carcinoma were included; 9 were client-owned, whereas 1 was a research colony dog. METHODS: Retrospective study. Serum miRNA was evaluated by RNA deep-sequencing (RNAseq) and digital droplet PCR (dPCR).Expression of candidate biomarkers miR-18a, miR-19b, miR-29b, miR-34c, miR-122, miR-125a, and miR-181a was compared with clinical characteristics, including grade, metastasis, and survival. RESULTS: 452 unique serum miRNAs were detected by RNAseq. Sixty-five individual miRNAs were differentially expressed (>±1.5-fold) and statistically significant between groups. Serum miR-19b (P = .003) and miR-125a (P < .001) were significantly higher in the mammary carcinoma group by dPCR. Both had high accuracy based on receiver operator characteristic area under the curve (0.930 for miR-125a; 0.880 for miR-19b). Circulating miR-18a by RNAseq was significantly higher in mammary carcinoma dogs with histologic evidence of lymphatic invasion (P = 0.03). There was no significant association with any miRNA and survival or inflammatory status. CONCLUSIONS AND CLINICAL IMPORTANCE: Circulating miRNAs are differentially expressed in dogs with mammary carcinoma. Serum miR-19b and miR-18a represent candidate biomarkers for diagnosis and prognosis, respectively.