Merkel cell carcinoma
Merkel cell carcinoma (APUdoma; multicentric cutaneous neuroendocrine carcinoma) are a rare benign neoplasm of the canine skin.
Merkel cells are mechanireceptors comprised of follicular epidermal and dermal neuroendocrine cells found throughout the skin, oral cavity, and internal organs, where they aggregate around dermal nerve terminals. Immunohistochemical studies have shown that these tumors behave more as neural, rather than basal, epithelial cells.
Although Merkel cell polyomavirus appears to initiate malignant transformation in humans, similar viruses have not been isolated in dogs, and the majority of canine cases are relatively benign.
In dogs, primary neuroendocrine tumors can arise in sites such as the intestines, esophagus, nasal cavity, skin, bile duct, gallbladder, liver (hepatic neuroendocrine tumor), and nasopharynx. Peritoneal carcinomatosis and metastasis to regional lymph nodes occurs frequently.
Diagnosis requires histological examination of biopsied material.
Histologically, these tumor locally effaces periadnexal and deep dermis tissue and comprise mainly clusters of membrane-bound dense-core neuroendocrine granules within the dermis.
In the majority of cases, surgical excision is curative and reports of metastases appear uncommon.
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