Basal cell carcinoma
As the name suggests, basal cells rest on the bottom of the epidermis (skin) and act as stem cells which can differentiate into a number of epithelial cells. Basal cells are mitotically active, but they lose this potential when they detach from the basement membrane and embark on the outward trek toward the skin surface. As basal cells migrate upward toward the surface, they enter the spinous layer, strengthen their cytoskeletal and intercellular connections and gain resilience to mechanical stress. Once this task is completed, the cells enter the granular layer, where they produce the epidermal barrier.
Although the etiology of basal cell neoplastic transformation is incompletely understood, carcinogens exposure is thought to trigger expansion of finite basal cell clonal lines (by inhibition of hedgehog signaling pathways), leading to various forms of epithelial tumors. It is the ubiquitous epidermal role of basal cells which complicates their manifestation in skin neoplasia in the dog.
Basal cell tumors frequently appear as a solitary, well-circumscribed, formed, hairless, raised mass in the skin, typically located on the dog's head, neck or shoulders.
Basal cells may also occur in mixed-cell tumors such as those found in the oral mucosa of the mouth (acanthomatous ameloblastoma) and epithelial lining of mammary tumors since they contain neoplastic basal cells acanthocytes and stellate cells.
Basal cell carcinoma are locally invasive, and may be recur locally or develop multicentrically but rarely metastasize systemically, unlike mast cell tumors. Basosquamous carcinoma, which are intermediate between basal cell and squamous cell carcinoma are more aggressive and may metastasize to internal organs.
Basal cell carcinoma have the histologic evidence of cornification, a feature they have in common with squamous cell carcinomas. Therefore, they are generally called basosquamous cell carcinomas. Visually, they appear as asymptomatic, firm, annular plaques with a raised border, making them difficult to distinguish from trichoepitheliomas.
Diagnosis is usually based on histological examination of biopsied skin samples.
A differential diagnosis would include sebaceous adenoma, chronic solar dermatitis, pilomatricoma, keratoacanthoma, papilloma, hepatoid gland carcinoma, mast cell tumor and squamous cell carcinoma.
Simple surgical excision is curative in most cases.
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