Cancer in horses: the risks and recovery rates

However, every year, more than 200 horses insured with Agria in Sweden are diagnosed with some form of cancer. In most cases, horses recover after treatment, particularly when a tumour is benign and detected early. However, some forms of cancer can be difficult to treat and carry a poorer prognosis. 

"The most common tumours we see in horses are skin tumours such as melanomas and sarcoids, but there are also more unusual and serious internal cancers," says Linda Dunbäck, an Agria veterinarian. 

Why grey horses are especially prone 

Melanomas are the most common skin tumours in grey horses, especially those over 15 years of age. They often appear as black or dark grey lumps, usually in the skin around the anus, under the tail, at the base of the ears, behind the jaw, or at the base of the mane. Larger tumours around the anus can make it difficult for a horse to pass droppings normally. 

Research from the Swedish University of Agricultural Sciences, supported by the Agria Research Fund, has shown that up to 80 per cent of grey horses older than 15 develop melanomas. This is thought to happen because melanin accumulates in the body as the horse's coat fades with age. 

These tumours are not always harmful, but it is important to monitor any new lumps, growths or areas of tenderness and seek veterinary advice if you notice changes. 

Sarcoids 

Sarcoids are the most common type of skin tumour found in horses. They are caused by a virus and most commonly appear on the inside of the thighs, behind the elbows, under the belly and around the sheath. 

Depending on their location, they can be both unsightly and physically troublesome. In some cases, they can interfere with tack or equipment and may become prone to bleeding or oozing. 

Particular problems for geldings and stallions 

Tumours on the horse's penis are often discovered at a late stage, which can make treatment both extensive and challenging. 

Make it a habit to inspect the horse's penis while he is urinating or when he has been given a sedative. This may help identify potential problems at an earlier stage, when treatment is often more straightforward. 

Lymphoma: malignant tumours 

Lymphoma is rare in horses but is the most common type of internal malignant tumour. The disease can present with a wide range of clinical signs, depending on which organs are affected. 

Equine lymphomas commonly affect multiple sites throughout the body (multicentric), but lymphomas affecting the skin and gastrointestinal tract are also among the most commonly diagnosed forms of the disease. 

Treating tumours 

Today, horses with cancer are mainly treated through surgery, where the tumour and surrounding tissue are removed. 

More advanced treatments, such as radiotherapy and chemotherapy, are available in some countries. Benign tumours can sometimes be left untreated if they are not causing discomfort or affecting the horse's quality of life. 

What's the prognosis for a horse with cancer? 

In many cases, horses recover well following surgical or medical treatment, particularly when a tumour is benign and diagnosed early. This is one of the reasons it is important to check your horse regularly for lumps and bumps, so that anything unusual can be identified as soon as possible. 

Many skin tumours, including melanomas and sarcoids, can be removed without affecting a horse's quality of life or ability to work and enjoy normal activities. 

However, some tumours can return after treatment, making ongoing monitoring and follow-up important. 

Thanks to Agria's unique lifetime equine insurance, veterinary fees for treatment relating to recurrent tumours may be covered, provided the policy was in place before the initial cancer diagnosis. 

In more unusual cases, such as internal cancers like lymphoma, the prognosis can be poorer because these conditions can be difficult to treat and may carry a higher mortality rate.