Skin tumours in the horse: clinical presentation and management

Diagnosing and managing skin tumour types commonly found in horses

source: Greg Quinn
In Practice vol 25 no 8, September 2003
starts p476, 7 pages long

Owners are likely to take their horses for treatment rapidly if they find skin tumours, because such tumours are easy to spot. Tumours are often very worrying for owners, and can present challenges for vets. Telling the difference between non-neoplastic and neoplastic conditions is not always easy, but it is important to make an accurate diagnosis, so that the treatment is appropriate. A histopathological diagnosis should be used, as well as assessing the history and symptoms of the horse. The whole of the horse's body should be checked, and fine needle aspiration and biopsies can help in diagnosing suspicious lesions. These diagnostic techniques should be used with caution, for example, chronic lesions that are ulcerated should not be sampled.

Lesions are especially common on the ears, eyelids and face, and in areas like the inner thighs where the skin is thin. Flies may be involved in the transmission of disease, through abrasions and wounds.

There are some six types of sarcoids, occult, verrucose, nodular, fibroblastic, mixed, and malevolent. Occult sarcoids have a scaly, grey surface, while more advanced sarcoids are called verrucose, with thickened skin. Nodular sarcoids are subcutaneous lumps, which fibroblastic sarcoids are firm masses that are ulcerated. Fibroblastic sarcoids may become malevolent, with the tumour invading along lymphatics.

Melanomas tend to affect grey horses, especially as they age. An estimated 80% of grey horses suffer from melanomas by the age of 15-years-old. Papillomas, or warts, are linked to equine papillomavirus. They may be verrucose or aural and genital, and genital lesions can spread from one horse to another. Juveniles tend to be affected by verrucose warts. Squamous cell carcinomas rank second of equine neoplasms. Ultraviolet light and penile smegma are among factors predisposing horses to such carcinomoas.

Treatment of equine tumours varies according to a number of factors, such as the tumour type, and cost. Verrucose and occult lesions may be left to be monitored rather than treated. The prognosis tends to be poorer if there are lesions in several places, or lesions are advanced. Treatment options include chemotherapy and surgery. Laser ablation is another option, though the equipment is expensive, and the efficacy of this treatment over the long term is unclear. The article discusses diagnostic and treatment procedures in greater detail.