Gene Expression and Immunohistochemical Analyses of c-Myc in Canine and Feline Soft Tissue Fibrosarcomas

Canine and feline fibrosarcomas are malignant tumors of mesenchymal origin showing histological, molecular, and clinical structures similar to their human equivalent. In human medicine, cellular myelocytomatosis (c-Myc) has already been proposed as a vital gene that regulates aggressive cell growth and is a predictive marker and possible therapeutic target in fibrosarcomas. The goal of this study was to evaluate c-Myc expression in canine and feline fibrosarcomas by gene and protein analyses and correlate its expression to the histological grading system of the examined cancers. Nineteen archival formalin-fixed and paraffin-embedded canine and feline sarcoma samples were recruited. Sixteen of them were determined to be canine and feline fibrosarcomas. The samples consisted of eight cutaneous samples, four eyelid samples, three oral mucosa samples, and one vulva sample. Histopathological examinations were performed to estimate histological type, differentiation, cellularity, and mitotic count. On each sample, immunohistochemical assessment and mRNA expression were performed using an anti-c-Myc antibody and a <i>c-Myc</i> primer. The differences in the immunoreactivity staining values and the relative folds of the <i>c-Myc</i> mRNAs were categorized using already recognized grading criteria and a statistical analysis was performed. Among all the tested canine and feline fibrosarcomas, 75% of the grade II fibrosarcoma cases and all of the grade III fibrosarcoma cases were positive for the c-Myc protein. Furthermore, the relative values of the <i>c-Myc</i> gene were up-regulated in grade III compare to grade I and II fibrosarcomas. The results demonstrated that c-Myc expression was significantly higher in grade III than in grade II and I (<i>p</i> ≤ 0.05) fibrosarcomas regarding protein and gene levels. In summary, this work provides evidence for the high expression of c-Myc in canine and feline fibrosarcomas and proposes a supposed relationship with poor prognoses as determined by grading systems.