Let-7b, miR-29b, and miR-125b as Potential Biomarkers for Differentiating Canine Mammary Carcinoma Histological Types

MicroRNAs (miRNAs) are short non-coding RNA molecules involved in post-transcriptional control. They are closely related to cancer-associated processes, making them promising candidates for diagnostic and prognostic biomarkers, as well as targets for cancer therapy. This study investigated the expression levels of let-7b, miR-29b, miR-125b, and miR-146 in normal and neoplastic canine mammary gland samples by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Furthermore, the miRNA profile of the tumors was compared to adjacent mammary glands and to normal control mammary tissues. MiR-29b and miR-125b were downregulated in both benign and malignant lesions compared to the control, while let-7b was significantly downregulated only in malignant lesions. Additionally, miR-29b was upregulated in the malignant group compared to the benign group. Regarding histological type analysis, miR-125b was downregulated in simple carcinomas compared to complex carcinomas, whereas let-7b and miR-29b were upregulated in complex and simple carcinomas compared to the other subtypes, respectively. MiR-29b has been shown to be able to differentiate malignant from benign, while miR-125b can discriminate simple carcinomas from complex carcinomas. In addition, let-7b, miR-29b, and miR-125b, together, can discriminate simple and complex histological types from other histological types. In conclusion, the present study demonstrated that the expression of these miRNA changes during the tumorigeneses process, representing an epigenetic mechanism to sustain canine mammary tumor development, and identified these miRNAs as promising diagnostic biomarkers.