Melanoma

A melanoma is a malignant tumour arising from the pigment cells (melanocytes) of the skin or mucous membranes. In dogs, melanomas can be benign or malignant – and that makes a huge difference. Malignant melanomas grow quickly and spread early. Preferred sites are the oral cavity, the paws and the skin. Because melanomas can metastasise rapidly, every week counts: Early diagnosis and treatment are crucial.

Origin and Biology

Melanomas originate from the cells that produce the pigment melanin – this is the colouring agent that tones skin, hair and mucous membranes. Many melanomas in dogs are indeed benign. Malignant ones, however, are a different story: they are extremely aggressive and can spread to the lymphatic system and internal organs, particularly the lungs.

Causes and Risk Factors

Why a melanoma develops is not yet fully understood. However, some risk factors are known:

• Genetic predisposition: Certain breeds are more frequently affected, including Schnauzers, Scottish Terriers, Poodles, Cocker Spaniels and Golden Retrievers.
• Pigmentation: Darkly pigmented dogs appear to carry an increased risk of developing melanomas.
• Environmental influences: Sun exposure can increase the risk of skin melanoma – however, this factor plays a lesser role in dogs than in humans.

Common locations of melanomas in dogs

Melanomas can occur throughout the body, but some sites are particularly frequently affected.

Oral melanoma

The oral melanoma is the most common form of malignant melanoma in dogs. It is located in the oral cavity – on the gums, on the tongue or in the palate. These tumours grow aggressively and metastasise early, usually to the lungs and lymph nodes.

Digital melanomas (paws)

Melanomas can also develop on the paws or nail beds. Such tumours are often painful; affected dogs limp or show swelling. Metastasis usually occurs to the lymph nodes or lungs.

Skin melanoma

Skin melanomas can be either benign or malignant. Benign forms often appear as dark, flat or slightly raised areas on the skin. Malignant skin melanomas follow a more aggressive course and can spread – this should not be taken lightly.

Clinical symptoms

The signs depend heavily on where the tumour is located:

Oral melanoma:

• Bad breath (halitosis)
• Difficulty eating or swallowing
• Bleeding from the mouth
• Visible swelling or tumours in the mouth area
• Increased salivation
• Weight loss

Melanoma on the paws:

• Lameness or difficulty walking
• Swelling in the area of the toes or nails
• Changes in colour or structure of the nails

Skin melanoma:

• Dark spots or nodules that grow or change
• Ulcers or open wounds that do not heal
• Hard or raised tumours

Oral melanomas, in particular, are often discovered late – simply because people rarely look inside a dog’s mouth. Regular oral examinations are therefore important, especially in breeds with an increased risk.

Diagnosis

To diagnose a melanoma, several examination steps are necessary:

1. Clinical examination: The vet palpates suspicious areas and looks for signs of metastasis – such as enlarged lymph nodes or breathing difficulties.
2. Fine-needle aspiration: Cells are taken from the tumour with a fine needle and examined under a microscope.
3. Biopsy: A tissue biopsy provides more precise information on whether the tumour is benign or malignant.
4. Imaging techniques:
   • X-rays or CT scans show whether metastases are already present in the lungs or other organs.
   • Ultrasound can make enlarged lymph nodes and other signs of tumour spread visible.
5. Blood tests: They provide information on the general state of health and possible effects on other organs.

Treatment options

Treatment depends on size, location, stage and the extent of any metastasis.

Surgical removal

• Surgery is the first choice – especially for skin and oral melanomas. The aim is complete removal with a safety margin to minimise the risk of recurrence.
• In the case of digital melanomas, amputation of the affected toe may be necessary. This sounds drastic, but it often allows the dog to live pain-free again.

Radiation therapy

• Radiation therapy is an option if the tumour cannot be completely removed surgically or if it is particularly aggressive. It can slow down growth and relieve pain.

Chemotherapy

• Melanomas generally respond poorly to chemotherapy, which is why it is used less frequently. However, in advanced cases or with metastases, it can be a supplementary option.

Immunotherapy (melanoma vaccine)

• A special melanoma vaccine has been developed for dogs, which supports the immune system in fighting tumour cells. It is frequently used for oral melanomas and can extend survival time – one of the most interesting developments in veterinary oncology in recent years.

Prognosis

The outlook depends heavily on location and stage:

• Oral melanomas: The prognosis is often unfavourable. These tumours grow aggressively and metastasise early. Even with intensive treatment, the average survival time after diagnosis is often less than a year – particularly if the lungs or lymph nodes are already affected.
• Digital melanomas: Whether complete removal with a safety margin is successful is decisive. As these tumours often metastasise, the prognosis is also limited.
• Skin melanomas: Benign forms have good chances of healing. With malignant skin melanomas, however, the risk of metastasis increases significantly – close follow-up care is important here.