Melanoma In Cats

The cells that determine a cat’s beautiful fur and eye color are called melanocytes. It hardly seems apt that these cells are also the source of melanoma, a type of cancer that becomes especially dangerous if not detected and treated early. Melanoma tumors form when melanocytes grow out of control. In addition to presenting as dark spots or tumors on the skin, melanoma can develop in a cat’s eyes or mouth. Fortunately, while melanoma is the most dangerous type of skin cancer for humans — primarily because it can spread aggressively — it is extremely rare in cats. Those that are stricken tend to be older. Neither a cat’s sex nor breed is a determining factor in the likelihood of developing melanoma.

Melanoma in cats is treatable but not always curable and it tends to return. The treatment course depends on the location of melanoma in the cat, and the prognosis typically will vary depending on numerous factors, including the type of melanoma, whether the cancer has metastasized (spread), the cat’s overall condition, how well he or she responds to treatment and other factors. It’s also important to note that some skin tumors, including those of melanocyte origin, are benign.

Types of Feline Melanoma

• Dermal Melanoma: Forms on the skin. Skin tumors could be benign or malignant. They may be raised masses or flat in shape.
• Oral Melanoma: Tumors form in the mouth. Oral melanoma can spread to the lymph nodes in the neck or to the lungs or liver.
• Ocular Melanoma: Forms in the eyes. The color of a cat’s eyes depends on pigments, which are produced by melanocytes.

Symptoms of Melanoma in Cats

Since early detection is a key to treating melanoma effectively, it’s important to know the signs that may present:

• In the case of dermal melanoma, you likely would be able to feel or see a mass on the skin or notice a flat discoloration.
• An oral tumor might cause your cat to drool or have bad breath. He or she may also have difficulty eating. This might manifest as chewing on only one side, cocking his or her head to eat, or eating only soft foods. Sometimes, a cat’s melanoma tumor in the mouth will be pigmented and look black, but that’s not always the case. Those that do not express a lot of pigment are called amelanoctic melanomas.
• With ocular or iris melanoma in cats, the colored part of the eye (the iris) may appear darkened. However, freckles can also occur in the iris, so your veterinarian or a veterinary ophthalmologist would have to determine what is causing the discoloration as freckles are benign condition.

Any abnormal growths on the skin or in the mouth or eyes would merit a trip to the veterinarian for further examination.

Diagnosing Melanoma in Cats

Tests to determine whether a cat has malignant melanoma are similar to the testing for other types of cancer. A physical exam can reveal not only the presence of a lump but its size, and veterinarians often check lymph nodes for any signs of swelling (even during routine exams). Your cat’s behavior also can provide clues about progression and whether the cancer is impacting the body’s systems. Blood work and urinalysis can help determine the overall health and organ function of your pet. Three view chest X-rays and possibly an abdominal ultrasound may be ordered to determine whether the cancer has spread to the lungs or liver. Additionally, depending on the location of the mass and whether it’s easily accessible, a fine needle aspiration can be performed to remove a sample of the suspicious tissue for further testing by a lab. Ultimately, biopsy (taking a piece of the actual mass) may be needed to obtain a definitive diagnosis.

Treatment Options and Prognosis

Different types of melanoma in cats call for different treatment plans.

Surgery

If a tumor is accessible and your cat is in good enough condition to handle surgery, then removal is often the best option. With surgery, the goal is to obtain clean margins, meaning the edges of the removed tissue are cancer-free — an indication that the malignant portion has been entirely removed. If a skin tumor is benign, removal could be curative. If it is malignant, then your cat’s medical team can assess the aggressiveness of the tumor to determine what the next steps might be. The problem with removal of a malignant tumor is that the cancer may still return in a matter of months, or it may not return over the course of a normal lifetime. Postsurgical radiation treatments may be recommended to hinder the chance of recurrence.

Enucleation

Enucleation is a specific type of surgery. It involves the removal of a cat’s eyeball in cases of ocular melanoma. The prognosis for a cat with ocular melanoma depends on different factors, including whether there has been vascular invasion (cancer cells growing into the blood vessels like the arteries and veins). A veterinary ophthalmologist should be consulted to determine a treatment course due to the level of expertise required.  For aggressive ocular melanomas, they may recommend seeing a veterinary medical oncologist.

Radiation

Radiation is designed to damage or kill cancer cells by directing high-energy particles at the targeted tumor while sparing surrounding healthy issue as much as possible. The two primary types of radiation are conventionally fractionated radiation therapy (CFRT) and the more innovative stereotactic radiation (SRS). The latter uses higher doses of radiation, with a much greater rate of precision and thus fewer treatments are needed — one to three treatments for SRS vs. 16 to 18 treatments for conventional radiotherapy. Stereotactic radiation can be extremely beneficial because radiation treatments require the cat to undergo anesthesia. Since anesthetic events carry their own additional risks, a treatment approach of “the fewer the better” might be the preferable option. Radiation may be recommended as the sole treatment or in addition to surgery. If surgery is ruled out for any reason and radiation is the treatment of choice, then stereotactic radiation could be the most beneficial.

Chemotherapy

Chemotherapy is not typically the primary treatment for melanoma in cats. However, if surgical removal of a melanoma tumor is not an option or was not curative, chemo may be recommended to help try to extend a cat’s quality of life. Chemotherapy may be used in very aggressive melanoma cases. To learn more, a consultation with a veterinary oncologist regarding the cat’s specific circumstances would be in order.

Melanoma Vaccine

In some circumstances, a melanoma vaccine designed to specifically fight these cancer cells might be used. A veterinary oncologist should make the call based on the cat’s type of cancer, stage and other factors.

Learn More About PetCure Oncology Treatments

PetCure Oncology specializes in treating cats with cancer, including melanoma. Our wide range of treatment options includes technologically advanced stereotactic radiation. We are committed to compassionate care in our mission to provide your pet with the best quality of life and extend your time together as long as possible. To learn more about our treatments, find a location near you and reach out today.

The contents of this article were provided in part by Dr. Renee Alsarraf, DVM, DACVIM (Oncology), a board-certified veterinary medical oncologist and member of PetCure Radiation Oncology Specialists (PROS).