Using GeLC-MS/MS, we discovered potentially novel candidate markers of canine oral tumors such as Jumonji domain containing 1C (JMJD1C or TRIP8) in benign tumors, inversin (INVS) and rho guanine nucleotide exchange factor 28 (ARHGEF28) in OM, BTB domain-containing 16 (BTBD16) in OSCC, and protein tyrosine phosphatase non-receptor type 1 (PTPN1), BRCA2, WW domain binding protein 2 (WBP2), purinergic receptor P2Y1 variant 2 (P2Y1) and proteasome activator subunit 4 (PSME4) in all cancerous groups. This evidence concerns the gene PTPN1 and benign neoplasm.