In this study, the healthy group presented a mean age lower than the tumor group, and despite what is reported in human and rats (58, 59), the results obtained demonstrated that cats with mammary carcinoma have a reduced Free Leptin Index (FLI) in comparison to the healthy group (p = 0.0006), not only due to the increase in serum ObR levels (60), but also suggesting that diseased animals may have decreased soluble leptin levels, as reported in pre-menopausal women with breast cancer (61) and colon cancer patients (62). This evidence concerns the gene LEPR and neoplasm.