Mammary carcinomas are aggressive neoplasms and a significant cause of mortality in female cats. Despite surgical removal, feline mammary carcinoma (FMC) often recurs or metastasizes. Specific tumour biomarkers are necessary for early detection, prognosis, and therapy selection. This study aims to identify candidate biomarkers for FMC by comparing tissue proteomic profiles among grades of 31 FMC cats and 6 normal mammary tissues (control) using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS).