Basal cell carcinoma

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Basal cell carcinoma, basal cell epithelioma and basaloid tumors are relatively common adnexal tumors of older dog skin characterized by malignant transformation of epithelial basal cells[1].

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[2]. 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[3]), leading to various forms of epithelial tumors[4]. 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[5]) and epithelial lining of mammary tumors[6] since they contain neoplastic basal cells acanthocytes and stellate cells.

Basal cell epithelioma and basaloid tumors are usually benign and tend to occur in older dogs, especially Cocker Spaniels and Poodles.

Basal cell carcinoma are locally invasive[7], 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[8].

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[9].

A breed predisposition for basal cell carcinoma has been reported in the Saint Bernard, Scottish Terrier and Norwegian Elkhound.

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[10].

Simple surgical excision is curative in most cases.

References

  1. Saridomichelakis MN et al (2013) Basal cell carcinoma in a dog with chronic solar dermatitis. J Small Anim Pract 54(2):108-111
  2. Tan DW & Barker N (2012) Stem cell reprogramming as a driver of basal cell carcinoma. Nat Cell Biol 14(12):1246-1247
  3. Von Hoff DD et al (2009) Inhibition of the hedgehog pathway in advanced basal-cell carcinoma. N Engl J Med 361(12):1164-1172
  4. Tang XH et al (2013) Basal Stem Cells Contribute to Squamous Cell Carcinomas in the Oral Cavity. Carcinogenesis [ Jan 28]
  5. Hatai H et al (2012) Spindle Cell Ameloblastic Carcinoma in a Labrador Retriever Dog. J Vet Med Sci Dec 10
  6. Ribeiro GM et al (2012) Morphological aspects and immunophenotypic profiles of mammary carcinomas in benign-mixed tumors of female dogs. Vet Med Int 2012:432763
  7. Simeonov R & Simeonova G (2010) Comparative morphometric analysis of recurrent and nonrecurrent canine basal cell carcinomas: a preliminary report. Vet Clin Pathol 39(1):96-98
  8. Shin SK et al (2011) Basosquamous carcinoma with systemic metastasis in a miniature Pinscher. Jpn J Vet Res 59(4):173-179
  9. Khelifa E et al (2013) Dermoscopy of Desmoplastic Trichoepithelioma Reveals Other Criteria to Distinguish It from Basal Cell Carcinoma. Dermatology Jan 30
  10. Weiss E, Frese K (1974) Tumours of the skin. Bull World Health Organ 50(1-2):79-100