What they are:

These are big, commonly dark-coloured masses that occur around the tail, genitals, mouth and throat-latch of mature grey horses. These tumours are usually benign and grow slowly, although in a small number of animals they will continue to be a problem and may even prove fatal. Owners typically notice a small nodule beneath the skin, but over time, often only over years, other nodules appear and the growths can join up to form a large mass that may ulcerate through the skin. Melanomas around the tail and anus commonly become ulcerated, and keeping these areas clean is important. The difficult thing with melanomas is that while most will remain benign, some will become malignant over time, and some start out malignant. The ones that become malignant will spread via the blood and lymph nodes to other sites in the body like the lungs, liver and spleen. If a melanoma starts out malignant it will usually spread very quickly.

Treatment: 

Many animals affected by melanomas will have long and successful lives and careers with the tumours impacting little if at all on their quality of life. However, some melanomas will need treatment because of malignancy or more commonly because they are in an inconvenient place. The treatment options for melanomas have varying levels of success. Small, solitary nodules can often be removed surgically, but this depends on the area and the surrounding structures. Some melanomas can also be removed by freezing (cryosurgery) but this has had very variable results, with treatments often needing to be repeated. Other methods of treatment include radiotherapy, chemotherapy and immune-mediated treatments – all of these modalities have variable degrees of success.