Expression of Leptin and iNOS in Oral Melanomas in Dogs

Background Oral melanoma (OM) in dogs is an aggressive malignancy, with clinical behavior resembling cutaneous melanomas in humans. Melanoma in humans is promoted by an inflammatory environment that is contributed to by leptin and inducible nitric oxide synthase (iNOS). Objective To determine if the patterns of leptin and iNOS expression are similar in OM in dogs and cutaneous melanomas in humans. Animals Twenty client-owned dogs. Methods Retrospective case study. Immunostaining of the OM tumors from each dog was scored for percentage and intensity of leptin and iNOS expression. Mitotic index was used as an indicator of tumor aggression. Results Leptin was detected in ≥75% of the tumor cells in specimens from 11 dogs. One tumor expressed leptin in ≤25% of the cells. The intensity of leptin expression was variable with 6, 9, and 5 cases exhibiting low-, moderate-, and high-intensity staining, respectively. OM with the lowest percentage of iNOS positive cells displayed the highest mitotic indices (P = .006, ANOVA). Conclusions and Clinical Importance The expression of leptin is a common finding in melanomas in dogs. These data suggest that the possibility of future clinical applications, such as measuring the concentrations of plasma leptin as a screening tool or leptin as a target for therapy. The relevance of iNOS is not as clear in dogs with OM, for which other directed therapeutics might be more appropriate.