Squamous cell carcinoma (SCC) is a common tumor in many domestic species (horses, cows, cats, and dogs). Sunlight is the most important carcinogenic stimulus for development of SCC, especially in lightly pigmented areas of animals with substantial exposure to sunlight. Peak incidence is in horses 13 years and older. In horses, it is the most common neoplasm of the eye and second-most common tumor of the horse overall. Draft horses, Haflingers, and Appaloosas are reported to be predisposed. Besides periocular locations, tumors of the perineum and vulva are also common. SCC goes through several stages of development, and early, premalignant stages may be difficult to detect. The tumors may be slow-growing at first, taking years to progress. In general, advanced lesions are locally aggressive and may metastasize to draining lymph nodes but rarely to distant tissues. Early detection and treatment are prudent to avoid advanced disease and complications.
See Ocular Neoplasia in Horses and Squamous Cell Carcinomas in The Vet Manual.
References
Bellone RR, Liu J, Petersen JL, et al. A missense mutation in damage-specific DNA binding protein 2 is a genetic risk factor for limbal squamous cell carcinoma in horses. Int J Cancer. 2017; 141(2):324–353. doi: 10.1002/ijc.30744.
Jeanes EC, Koll–Hampp S, Dawson C, et al. Rhomboid blepharoplasty and cryotherapy for the treatment of a squamous cell carcinoma on the lower eyelid in a horse. Clin Cas Rep. 2018;7(1):40–46. doi: 10.1002/ccr3.1907.
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