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Keywords:

  • horse;
  • squamous;
  • tumour;
  • chemotherapy;
  • photodynamic

Summary

Squamous cell carcinoma (SCC) accounts for approximately 20% of all equine mucocutaneous (MC) tumours and continues to present a therapeutic challenge to practitioners. Most MC-SCC are locally invasive and slow to metastasise, but metastasis to local lymph nodes is not uncommon. The most common location for MC-SCC is the periorbital region, with the eyelid most commonly affected. Although only 13% of MC-SCC involves the external genitalia, MC-SCC is the most common neoplasm of male genitalia. Equine caballus papillomavirus-2 has recently been linked to MC-SCC and may prove to be necessary for tumour development. Risk factors may include chronic exposure to ultraviolet light and chronic skin irritation. Horses developing genital MC-SCC tend to be older compared to those with periorbital MC-SCC. Histopathology is required for definitive diagnosis of MC-SCC, although horse phenotype and lesion location may suggest MC-SCC. Several treatment modalities have been successful in eliminating or managing MC-SCC, with surgical excision and intratumoural chemotherapy yielding the best results. Other treatment options including cryotherapy, hyperthermia, radiotherapy and photodynamic therapy are often used as adjunctive therapies. Early recognition of tumours and prompt intervention are associated with a positive outcome.