LAUSR

OBJECTIVE To investigate putative associations between oral melanoma size and variables of histologic grade such as mitotic index, nuclear atypia, junctional activity, ulceration, lymphatic invasion, and degree of pigmentation. SAMPLE 59 samples of oral melanomas from dogs sourced from 6 diagnostic laboratories within Australia. PROCEDURES The size of each melanoma was microscopically measured, and each sample was evaluated for variables of histologic grade including mitotic index, nuclear atypia, junctional activity, ulceration, lymphatic invasion, and degree of pigmentation by a veterinary pathologist. The association between tumor size and histologic outcomes was then statistically evaluated. RESULTS A significant relationship was identified between the size of oral melanomas and a single variable of histologic grade, lymphatic invasion, with larger tumors more likely to show lymphatic invasion. Further analysis revealed 2 applicable size thresholds for different clinical scenarios. Results indicated lymphatic invasion can confidently be ruled out for tumors < 6.5 mm in diameter (100% sensitivity) and ruled in for tumors ≥ 24.5 mm in diameter (100% specificity). CONCLUSIONS AND CLINICAL RELEVANCE An association was found for oral melanomas of dogs between tumor size and lymphatic invasion.