Current Concepts

Oral Malignant Melanoma in Dogs and Cats

Melanoma is a tumor of melanocytes, which arise from neural crest cells and function to synthesize melanin. Melanocytes are commonly located in the oral cavity, haired skin and eye, making these the most common locations where melanomas arise. Biologic behavior of melanoma depends in part on tumor location. The majority of melanomas that arise in the oral cavity are classified both histologically and biologically as malignant. Histologic features that support a diagnosis of oral malignant melanoma include a mitotic index greater than 2 mitoses per 10 high-powered fields, nuclear atypia, vascular or lymphatic invasion and ulceration. Malignant tumors may be variably pigmented or amelanotic (one third of cases). Since melanocytes are derived from neural crest cells, which ultimately give rise to both glandular tissues and connective tissues, melanomas can resemble both carcinomas and sarcomas morphologically. Given these challenges to diagnosing a malignant melanoma, several immunohistochemical stains have been developed to aid in the diagnosis.  Melanomas typically stain positive for vimentin, melan A, S100, and neuron-specific enolase (NSE); these stains can be helpful in diagnosis. Continue reading