Melanoma in Cats
Melanomas are tumors of pigment-producing cells known as melanocytes. These abnormal growths can be benign or malignant. Although melanomas are quite rare in cats, they can still be a cause for worry because they tend to be very invasive, recurring even after surgical removal. These tumors are also extremely aggressive. They can metastasize or spread to other areas of the body. Any pigmented growth on your cat’s body should be reported to the vet. You should be particularly concerned about specific areas where these melanomas classically developed - the eyes, mouth, and skin. Keep reading to learn more!
Types of Melanoma in Cats
Melanoma can develop in any part of the body where melanocytes are present. The behavior of malignant melanoma depends to a large extent on the part of the body where it develops.
There are several areas of the body where particularly invasive melanomas develop. These tumors are not only locally destructive but can easily spread to major organs of the body, such as the lungs and liver. Melanomas in cats that are particularly threatening usually occur in the mouth and lips, toe or paws, and the eye.
There are three types of melanoma in cats - ocular, oral, and dermal.
- Ocular (Eye) Melanoma - this type of melanoma involves the eyes and tends to be more malignant compared to those in the mouth or skin. It’s the most common type of melanoma in cats, and the incidence is more common in cats than in dogs.
- Dermal (Skin) Melanoma - Most melanomas of the skin are benign and are called melanocytomas. These tumors are usually found on the areas of the body that are covered with skin. However, not all pigmented growths on the skin are benign. Many skin melanomas that behave in a benign manner have been found to be malignant after microscopic evaluation. Thus, it’s very important for any pigmented growth on your cat’s skin to be brought to the attention of your vet.
- Melanoma of the Mouth (Oral Melanoma) - Melanomas that develop in the mouth are highly malignant tumors. This means they can destroy oral tissues and quickly spread to other parts of the body. The tumors usually have a cauliflower-like appearance because of their irregular surface. They can occur anywhere inside the oral cavity, including the palate, tongue, and tonsils.
When a cat has oral melanoma, there are three important aspects of concern - the local destruction of tissues in the mouth, metastasis, and cancer in the organs where the melanoma has metastasized. Thus, chest x-rays are performed to check for evidence of spread, samples of local lymph nodes are obtained and examined microscopically, and an ultrasound exam is used to screen the abdomen.
Staging of Melanoma
The staging process is an important part of the diagnosis and treatment of malignant melanoma in cats. When the extent of tumor spread is determined, the prognosis can also be predicted. Chest x-rays, lymph node sampling, and abdominal ultrasound exams are checked for any evidence of metastasis (spread) of the tumor to other parts of the body.
The size of the tumor is an extremely important factor when considering the prognosis. The World Health Organization (WHO) staging system has been adopted by veterinary medicine in the staging of cancer in pets.
- Stage I - The tumor is less than 2 centimeters (cm) in diameter
- Stage II - The tumor is 2-4 centimeters (cm) in diameter
- Stage III - The tumor is 4 centimeters (cm) or larger; local lymph node involvement may or may not be present.
- Stage IV - There is evidence of tumor metastasis to distant parts of the body.
Prognosis of Malignant Melanoma in Cats
If your cat has been diagnosed with malignant melanoma, the odds of survival are not all good. Being an aggressive type of cancer, patients generally have a guarded prognosis.
Treatment Options for Cats with Malignant Melanoma
Depending on the tumor, treatment may only be local, or extensive treatment may be necessary if cancer has spread to other areas in the body (such as in cats with Stage IV melanoma).
Surgical removal is generally the best initial step to take. The tumor’s size and location will determine if the main tumor can be completely removed or not. If surgery is unable to remove the entire tumor, adjunctive treatment is often performed.
Adjunctive therapy regimens in cat melanoma are given to extend the survival time. These treatment procedures include radiation, chemotherapy, or immunotherapy.
- Radiation therapy is the treatment option of choice if the tumor has not been completely removed, or the location or size of the tumor makes surgery not possible.
- Chemotherapy after surgery and/or radiation treatment may also be an option.
- Immunotherapy involves stimulating an immune response and triggering an attack on the tumor cells.
Like other malignant forms of cancer, treating malignant melanoma is geared towards controlling it and slowing down its progress, rather than expecting to cure the problem.
Is there a vaccine for feline melanoma?
A melanoma vaccine has been used for cats and dogs for several years now. The vaccine was initially developed for dogs. A study that evaluated the safety of the canine melanoma DNA vaccine in cats diagnosed with melanoma showed that the vaccine can be safely administered to cats with minimal risk of adverse effects.
The melanoma vaccine is not used to prevent the development of the tumor but to stimulate the body to mount an active immune response against the tumor. The vaccine helps identify the cancer cells so they can be attacked by the immune system.
Survival times of cats treated with the melanoma vaccine following surgical removal of the tumor were significantly improved compared to cats that only had surgery.
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