Background and aims <p>The development of breast cancer exhibits a heterogeneous and complex character in both felines and humans, which motivates the search for serum biomarkers for diagnosis, prognosis, and therapeutic monitoring. Although the feline species is recognized as a relevant comparative model for human breast cancer, metabolomic studies in cats are still scarce. This work aimed to investigate altered serum metabolites involved in feline mammary carcinoma (FMC).</p> Methods <p>Serum samples from 28 adult female cats (11 healthy and 17 with malignant mammary tumors undergoing mastectomy) were evaluated. The samples were extracted with pure methanol and derivatized (oximation followed by silylation) for GC–MS analysis.</p> Results <p>Twenty-six metabolites or chemical classes were found significantly altered. The main alteration was related to the metabolism of amino acids, carbohydrates, and the tricarboxylic acid cycle, mostly with reduced serum levels in female cancer patients, suggesting high tumor uptake. Analysis of metabolic pathways revealed alterations in the metabolism of alanine, aspartate, and glutamate; arginine and proline; starch and sucrose; and butanoate metabolism.</p> Conclusions <p>These findings provide preliminary evidence supporting the determination of candidate biomarkers and the mapping of disrupted metabolic pathways in FMC. Validation of the study and confirmation of the metabolite’s structural identity are critical to enable robust comparative studies and to direct the development of innovative diagnostic and therapeutic strategies.</p>