Melanoma in grey horses: what you need to know

What exactly is a melanoma?

A melanoma is a tumour that develops from pigment cells, known as melanocytes. In grey horses, these cells accumulate because the pigment in the skin disappears as the horse ages and turns grey. That process is accompanied by increased activity of the melanocytes, which raises the risk of tumour formation. Most melanomas in horses are initially benign, but can become malignant over time and spread to lymph nodes or internal organs. Dark or near-black lumps under the skin are the classic presentation.

Typical locations on the body

Melanomas appear on grey horses in virtually fixed locations. Check your horse regularly in the following places:

• Underside of the tail and around the anus (by far the most common location)
• Around the sheath or udder
• Groin and inner thigh
• Eyelids and ear margins
• Lips and corners of the mouth

When does a melanoma become dangerous?

A solitary, small lump that remains unchanged for years usually gives little cause for concern. Danger arises when tumours grow rapidly, clump together into large masses, or exert pressure on surrounding structures. A melanoma the size of a plum near the tail base can obstruct defecation or urine flow. Internal melanomas in the abdominal cavity or chest produce vague symptoms such as weight loss, colic symptoms, or reduced performance. Always have a vet examine any existing lump that grows noticeably larger in a short time, shows bruising, or begins to ulcerate.

Treatment options at a glance

• Watch and monitor: for small, stable tumours this is often the best approach
• Surgical removal: effective for isolated, easily accessible tumours
• Cimetidine: oral medication that inhibits growth in some horses; results vary
• Immunotherapy (e.g. intralesional injections): increasingly used — ask your vet about the latest options
• Radiation or laser treatment: available at specialist clinics, particularly for eyelid melanomas

Keeping track yourself: practical tips

Consistent monitoring is the key. Photograph new or existing melanomas every two to three months from the same angle, with a ruler or coin in the frame for scale reference. This allows you to objectively see whether a tumour is growing. In the horse profile of EquiSight you can save photos by date and add notes, so that you always have a clear timeline ready for every vet consultation. Also record the exact weight and any behavioural changes in the EquiSight diary, as a melanoma can have a subtle effect on your horse's wellbeing.

Genetics and breed predisposition

Not every grey horse carries the same level of risk. The STX17 gene, which is responsible for the grey coat, is also directly linked to the increased risk of melanomas. Horses that are homozygous for this gene (two copies) turn fully white more quickly and develop melanomas more frequently and at an earlier age than heterozygous animals. Lipizzaners, Arabians, and Camargue horses are disproportionately represented in the statistics. Do you know the genetic status of your grey horse? Have it established through a DNA test and record the result in the horse profile as a long-term reference.

EquiCoach helps you recognise patterns

Are you unsure whether a change you notice is normal? The intelligence behind EquiCoach can, based on your input — such as growth rate, location, and your horse's behaviour — indicate whether a vet consultation should be a priority. EquiCoach does not replace a veterinary diagnosis, but it does help you ask the right questions and ensure nothing is overlooked. That way you always stay one step ahead.