Merkel cell tumors are a rare cutaneous tumor in dogs and cats.
Etiology and Pathogenesis of Merkel Cell Tumors in Animals
Merkel cell tumors (cutaneous neuroendocrine carcinomas) arise from Merkel cells, neuroendocrine cells widely dispersed in the body and normally found in skin. Merkel cell polyomavirus has been implicated as a cause of Merkel cell carcinoma in humans.
Epidemiology of Merkel Cell Tumors in Animals
Merkel cell tumors are rare but have been documented in dogs and cats.
Clinical Features of Merkel Cell Tumors in Animals
Clinical manifestations of Merkel cell tumors may include multiple skin masses. Metastasis may be widespread.
Diagnosis of Merkel Cell Tumors in Animals
A presumptive diagnosis of Merkel cell tumors can be made based on signalment, history, clinical signs, and physical examination findings. Important differential diagnoses include lymphoma, plasmacytoma, and histiocytic tumors.
Histopathologically, Merkel cell tumors can be differentiated from canine cutaneous histiocytoma on the basis of the presence of argyrophilic cytoplasmic granules and positive staining for neuron-specific enolase, synaptophysin, and chromogranin A.
Treatment and Prognosis of Merkel Cell Tumors in Animals
Treatment recommendations for Merkel cell tumors consist of wide surgical excision.
Most Merkel cell tumors in dogs are benign. In contrast, Merkel cell carcinoma in cats is associated with a poor prognosis, with frequent occurrence of metastasis to regional lymph nodes and distant organs.
Merkel cell tumors may manifest as multiple skin masses.
Merkel cell carcinoma in cats carries a poor prognosis.