What is melanoma in dogs?

Melanoma is a type of tumor that arises from melanocytes, which are black-pigmented cells. Due to its origin from pigmented cells, these tumors are generally dark in color, but in some cases, amelanotic (without dark pigment) tumors may appear pink. While melanoma may grow locally, it can also spread to other parts of the body such as regional lymph nodes or the lungs if it is malignant.

When melanoma occurs in certain areas such as the mouth, lips, vulva, perianal region, digits, or nailbed, it is more likely to be malignant. However, if it appears on hairy skin, it is more likely to be benign. In the case of melanoma in the eye, most are benign, but there is a possibility that malignant tumors may also develop.

For the treatment of melanoma, the first option considered is surgical removal if viable. Afterward, chemotherapy or radiation therapy may be administered if necessary. Another option is a melanoma vaccine, which is a form of immunotherapy that may also be considered.

Causes of melanoma in dogs

Melanoma is a type of skin cancer whose root cause is still unknown. However, it has been established that multiple factors, including environment and genetics, play a role in its development. Although frequent exposure to UV rays has been linked to higher incidence rates in humans, it remains unclear how it impacts dogs.

Studies have shown that certain dog breeds, such as poodles, cocker spaniels, golden retrievers, schnauzers, and chow chows, have a higher incidence of melanoma. More research is needed to confirm this finding and shed light on the underlying causes of melanoma in dogs.

Symptoms of melanoma in dogs

Melanoma can appear with a variety of symptoms depending on its location and size.

Oral melanoma

Oral melanomas are a common type of melanoma in dogs, with 80% of cases occurring in the oral cavity. These tumors are often solitary and can be found in dogs aged 10 years and older, with small breeds being at higher risk. While some tumors may exhibit dark pigmentation and appear black, others may be pink or have mixed coloring. Dogs with oral melanomas typically present bad breath or a protruding mass, while others are diagnosed during dental prophylaxis. Despite being solitary tumors, they are highly aggressive and can invade surrounding tissues and bone, and metastasize to local lymph nodes and lungs. Identification of these tumors can be tricky, as they may appear as flat, plaque-type lesions.

Nailbed melanoma

The second most common location for melanoma in dogs is the nailbed or subungual crest, accounting for 15-20% of cases as solitary lesion. This type of melanoma can cause lameness, swelling, bleeding, or discharge from the affected toe, and may erode the bones of the toenails, resulting in significant pain. Metastasis rates are similar to oral melanomas, and initial staging should include careful evaluation of local draining lymph nodes such as the superficial cervical and axillary nodes for front foot tumors and the popliteal nodes for hind foot tumors.

Dermal melanoma

Dermal melanomas are often darkly pigmented dermal masses that may appear as single or multiple lesions, and in rare cases, may invade subcutaneous tissues. While those confined to haired skin are usually benign, certain characteristics on a biopsy report can indicate more aggressive behavior, and any melanoma occurring on a mucocutaneous junction has a higher potential to behave aggressively. Melanomas on the armpits and legs are typically benign, but those on mucocutaneous junctions, such as the vulva, anus, and lips, are more likely to be malignant and invasive, growing rapidly into surrounding tissues. Tumor location and biopsy results are important in determining the need for additional therapy after surgical removal.

Ocular melanoma

Two major types of melanoma occur in the eye: uveal melanoma and limbal melanoma.

• Uveal melanoma

  Uveal melanoma is the most common ocular tumor in dogs, and develops in the uvea, comprising the iris, ciliary body, and choroid. While most uveal melanomas are benign, they can cause pupil deformation and congestion as they grow locally and may lead to the development of uveitis and glaucoma. The mitotic index can be a useful predictor of clinical behavior. Up to 95% of uveal melanomas are anterior and involve the iris and/or ciliary body.

• Limbal melanoma

  Limbal melanoma occurs in the limbus, cornea, or sclera, and may result in conjunctivitis or keratitis. Most conjunctival and some eyelid and uveal melanomas are malignant. If ocular melanoma is present, you may notice brown or black spots or lumps in your dog's eye, and your dog may experience eye rubbing or excessive tearing.

Malignant melanoma in other places of the body also has the potential to metastasize to the eye.

What is the risk of melanoma in dogs

If a black tumor is observed on any part of a dog's body, it is important to visit the hospital for an examination regardless of the presence or absence of other abnormal symptoms. Melanoma in the oral cavity is particularly risky, with a high risk of malignancy, while melanoma in the toes can cause severe pain and potentially metastasize to other parts of the body. It is crucial to get checked out because melanoma can sometimes present as a non-pigmented tumor that may not appear entirely dark or black. Even if the tumor is not black, it is still essential to check any masses that are larger than 1 cm.

Are there any home treatments for melanoma in dogs?

If a tumor is confirmed, it is important to receive an accurate diagnosis and action plan from your veterinarian.

Excessive licking or chewing of the area can lead to secondary infection, so it is recommended to put a neck collar on your dog. This also helps to keep the affected area clean and avoid any further irritation or pain until you can take your dog to the vet.

Diagnosing melanoma in dogs

Diagnosing melanoma can be simple or complex depending on the type of tumor.

• Physical examination

  A fundamental aspect of a physical examination is to assess the size of the tumor and verify the presence of any swollen lymph nodes. It is important to ensure that there are no other tumors in different areas of the body, such as the mouth, eyes, or skin.

• Fine needle test (FNA) & Biopsy

  FNA, or fine-needle aspiration, is a technique used to evaluate the cytological features of a tumor. This involves puncturing the tumor with a needle and observing the cells that protrude under a microscope. The presence of melanin pigment in the cells makes it easy to diagnose.

  Pigmented melanoma poses a challenge in terms of diagnosis as relying solely on cytology may not suffice. A biopsy may be considered to confirm which type of tumor is present, by surgically removing a part of the tumor and examining it under a microscope. In some cases, special staining of the removed tissue may be necessary for confirmation as well.

  Histopathology through biopsy is a crucial step in determining the type and malignancy of the tumor. If there is a suspicion of metastasis to the regional lymph nodes, further evaluation of the stage of the tumor can be performed through fine-needle aspiration or biopsy of the lymph nodes.

• Blood test

  Although a blood test is not required to diagnose melanoma, it may be necessary to evaluate the dog’s overall health before starting certain treatments. A CT scan and a basic blood count test are also essential before administering anesthesia for surgical treatment.

• X-ray

  X-rays are utilized to examine the degree of invasion of the tumor into surrounding tissues, including bone or muscle, in the specific area where the tumor is located.

  Oral tumors are also known for their high invasiveness and tendency to metastasize to the lungs, making chest radiography necessary. Additionally, if there is suspicion of metastasis to organs in the abdominal cavity, abdominal radiography may also be conducted.

• CT scan

  If metastasis cannot be definitively confirmed through an X-ray, or if a more precise evaluation is required, a CT scan can be utilized to assess the presence of metastasis in the surrounding area, lungs, and lymph nodes. This imaging technique is more sensitive and can provide a clearer picture of any potential spreading.

Treatments for melanoma in dogs

Treatment of melanoma aims to remove the tumor before it grows larger and spreads or to control it if it has already spread.

• Surgery

  The most basic treatment for melanoma is surgical removal, which can vary depending on the location of the tumor. If the melanoma is on the skin, it can typically be removed easily in that area. However, if the melanoma is on a toe, the entire toe may need to be removed, or even the jawbone if it is in the mouth. Similarly, for a tumor on the eye, only the affected area may need to be removed if it is small, but if a local invasion is severe or there is intraocular hemorrhage or glaucoma, the entire eyeball may need to be removed.

  When the tumor is completely removed by surgery without metastasis, your dog can lead a healthy normal life without affecting their quality of life. However, if the tumor is located in a hard-to-remove area like under the tongue, additional treatments are necessary to reduce the tumor's size through surgical resection and slow the rate of re-growth. In cases of metastasis to regional lymph nodes, the lymph nodes must be removed if possible. If metastasis to other organs such as the lungs is likely or has occurred, additional treatments are required.

• Radiation therapy

  Radiation therapy is a commonly employed medical treatment to decrease the size of a tumor, especially if it is located in a difficult-to-remove position or is too large to be excised surgically. In some cases, even if a portion of the tumor has been surgically removed, radiation therapy may still be used to prevent the remaining tumor from regrowing.

• Melanoma vaccine

  Oncept® is a melanoma vaccine that can be used as a single treatment, but it is typically administered after reducing the size of the tumor through surgical removal or radiation therapy. This vaccine stimulates the body's immune system to attack melanoma, and it can also be used in conjunction with other treatments to relieve exacerbations, even if metastasis is likely or has already occurred.

  During the initial treatment with Oncept®, four treatments are administered every two weeks, followed by an additional vaccine every six months. When used in combination with surgical removal, this vaccine has shown a good therapeutic response, including increasing survival time and slowing tumor regrowth.

  However, it is important to note that, like surgical removal and radiation therapy, Oncept® does not guarantee a complete cure for melanoma, and the tumor may grow locally again depending on the patient. Therefore, regular check-ups are necessary to monitor progress and ensure timely interventions.

• Chemotherapy

  Chemotherapy is not generally considered a first-line treatment option for canine melanoma. However, despite the various treatments mentioned above, it can be considered if it continues to recur or metastasize and there is no response to treatment.

Preventing melanoma in dogs

Early detection and treatment are vital in combatting melanoma from worsening due to unclear causes for this disease to develop. It is advised to undergo periodic health checkups to ensure any signs of melanoma are detected and treated promptly.

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