[Written by a Veterinarian] What is Feline Malignant Melanoma? Symptoms, Treatments, and Early Detection Tips Explained

Among the malignant tumors that can affect cats, there is one known as malignant melanoma. While common in dogs, it is a rare tumor in cats. This tumor is known to metastasize easily. In this article, we will explain about malignant melanoma in cats.

What is malignant melanoma?

A tumor caused by the cancerous transformation of melanocytes (pigment cells)

Malignant melanoma is the cancerous transformation of melanocytes. Melanocytes are cells that produce a pigment called melanin, which protects cells from damage by ultraviolet rays. The cause of malignant melanoma is unknown.

Relatively rare in cats, but can occur in the mouth, eyes, and skin

Melanomas arise in tissues where melanocytes are distributed. Since melanocytes are found in the eyes, mouth, skin, and toes, these tissues are common sites for their occurrence. It is common in dogs but rare in cats.

Explanation of the difference between benign and malignant

Melanomas can be malignant or benign. Benign ones do not metastasize or spread, and can be cured by excision. Malignant ones tend to metastasize and grow rapidly. Even after excision, they may recur.

While skin melanomas are often benign, those that develop on the claws tend to be highly malignant. Additionally, melanomas that form in the eyes or mouth are often malignant.

Main symptoms of malignant melanoma noticed by owners and common locations

Black lumps or raised lesions

Skin melanomas typically appear as black, firm, hemispherical protrusions with hair loss. They may bleed or ulcerate, and can sometimes be accompanied by infection. Malignant cases grow rapidly.

Abnormalities in the mouth such as ulcers, bleeding, and drooling

Oral melanomas form masses in the mouth, which bleed persistently. Saliva mixed with blood or pus may also be present, and bad breath becomes stronger. If the mass is large, the mouth may not close, making it difficult to eat food or swallow.

Cases occurring on the toes or in the eyes

They can also occur on the toes, claws, or in the eyes, and are often malignant, especially when on the claws or in the eyes. In the case of toes or claws, the affected area may swell, and the claw may deform. Ocular melanoma can cause pigmentation on the rim of the iris. If it occurs inside the eyeball, the eye may become enlarged or deformed.

Difficult to distinguish from other skin conditions

Although malignant melanoma typically appears black, it can sometimes lack black pigment or present as red swelling. Therefore, it is a tumor that is difficult to diagnose solely by appearance.

Diagnosis methods and examination flow for malignant melanoma

Reasons why visual inspection alone is insufficient

Melanoma resembles other skin conditions and tumors. Additionally, melanoma in the eye can occur in unseen areas, so visual inspection alone is insufficient for diagnosis. Diagnosis always requires taking a tissue sample and performing a histopathological examination.

Fine-needle aspiration cytology, excisional biopsy, and histopathological examination for definitive diagnosis

Diagnosis of melanoma requires the detection of tumor cells. While skin melanoma can sometimes be diagnosed by fine-needle aspiration cytology, for oral or ocular cases, an excisional biopsy of the lesion is performed, followed by a histopathological examination for a definitive diagnosis.

Imaging tests are performed to check for metastasis

Melanoma can metastasize to nearby lymph nodes, but it can also spread to distant sites. A tumor in the mouth might metastasize not only to the jaw's lymph nodes but also to the lungs. Since melanoma itself can be difficult to discover or diagnose, and detection can take time, metastasis may have already occurred. Therefore, imaging tests such as X-rays, ultrasounds, and CT scans are performed to check for metastasis.

Main treatment methods for malignant melanoma

Surgical removal

Surgical excision is typically the first consideration for melanoma treatment. Complete removal can sometimes lead to a cure. However, melanoma progresses rapidly and infiltrates surrounding tissues, requiring extensive excision. Despite this, there remains a possibility of recurrence and metastasis. The excision area is quite wide, and in some cases, bone may also be removed. For example, if it's on a claw or paw skin, digit or limb amputation might be performed; if it's in the eye, enucleation; and if it's in the mouth, removal of the mandible or maxilla.

Surgical intervention is not only aimed at achieving a cure but also at improving the quality of life temporarily. For instance, in cases of oral melanoma where eating becomes impossible or breathing difficulties arise, debulking surgery is performed to reduce the tumor size.

Radiation therapy may be used in areas where complete excision is difficult

Radiation therapy is used when the tumor is extensive, cannot be completely removed, or has metastasized. Although melanoma is generally resistant to chemotherapy, it can respond to radiation therapy, so it may be used in combination with surgery. Radiation therapy involves multiple sessions, such as 12 times, to irradiate the tumor. During irradiation, radiation is targeted only at the tumor, so animals are placed under general anesthesia. Therefore, it is a considerably expensive treatment.

Post-treatment follow-up and QOL maintenance care are also important

After melanoma treatment, especially with surgery, extensive removal may be necessary, sometimes leading to the amputation of a digit, limb, or eye. Cats typically can live normally after such procedures, but due to the high likelihood of recurrence, regular veterinary visits are necessary.

If an oral melanoma is removed, part of the jawbone may also be removed, which can make it impossible for the cat to eat on its own. In such cases, a feeding tube is inserted into the esophagus during surgery to allow for liquid food administration.

Moreover, if the tumor was large, complete removal is often not possible, and some symptoms may persist even after treatment. For instance, bleeding, infection, and pain may occur, necessitating symptomatic treatment. If radiation therapy was performed, radiation-induced damage may also arise. Anesthesia carries risks, and radiation can cause dermatitis, hematopoietic disorders (bleeding, infection, anemia, etc.), and cataracts if the affected area is near the eyes.

Melanoma is a tumor with potential for metastasis and recurrence, thus regular check-ups are necessary. If other symptoms are present, it is also necessary to stabilize the condition with symptomatic treatment. If an esophageal catheter is placed, attention must be paid to ensuring adequate nutrition and preventing infection at the catheter insertion site.

Early detection saves lives: Daily observation tips for owners

Regularly check often-overlooked areas such as the mouth, between the toes, and ears

Melanomas can appear in areas that are difficult to see thoroughly, such as the mouth, between the toes, and ears. Therefore, they are often noticed only after they have grown larger. Make it a habit to check these areas regularly. Since it can be difficult to examine the inside of the mouth, it is advisable to have it checked during health examinations.

Don't overlook small lumps or pigmentation

The prognosis of melanoma changes significantly with early detection and treatment. Even if it starts small, it can grow rapidly, so it's crucial to diagnose and treat it before it gets large. Many cases are not visible, and some may look like simple spots. Do not assume it's just a spot; if it grows, always seek medical attention. Also, it may not always contain black pigment. It is important not to assume it's harmless just because it's not black.

Screening with annual to bi-annual health checks

Annual or bi-annual health check-ups are crucial for early detection of diseases. While it's difficult to find malignant melanoma during a general health check, abnormalities may be noted during oral or eye examinations. Regular annual health check-ups will also help owners understand what to watch out for. Therefore, make sure to schedule regular health check-ups.

Summary

Malignant melanoma progresses rapidly, growing quickly and potentially metastasizing. Starting treatment as early as possible may offer a chance for a cure. If you find a lump, do not hesitate to visit a veterinary clinic.