Cats can develop melanoma, a tumor arising from melanocytes, the cells responsible for producing the pigment melanin. While this cancer is less common in felines than in dogs or humans, it presents a health concern, particularly in older cats. Melanomas are classified as either benign (melanocytoma) or malignant, and the tumor’s behavior depends heavily on its location.
Where Feline Melanoma Appears
Feline melanoma frequently develops in a few distinct anatomical sites, and the location largely dictates the tumor’s likely behavior. Ocular melanoma is the most common form in cats, originating from the pigment cells within the eye, specifically the iris. These eye tumors are frequently malignant, though they tend to progress slowly, often over years, which allows for careful monitoring in early stages.
Oral melanoma is another site of development, appearing in the mouth on the gums, tongue, or lips. This form is aggressive and often malignant, posing a serious threat due to its tendency for rapid growth and spread. Oral melanomas can be destructive to the surrounding tissue.
Cutaneous melanoma, which affects the skin, is the least common type of feline melanoma. Skin melanomas most often appear on the head, ears, neck, or lower legs, and these are often benign, or melanocytomas. A rare but invasive form, subungual melanoma, can arise in the nail bed or toe, and these lesions are generally malignant and locally destructive.
Recognizing Observable Symptoms
The visible signs of melanoma vary significantly depending on where the tumor originates, making regular physical checks of your cat important. In the eye, the earliest sign of ocular melanoma is often a change in the iris, appearing as new, progressive darkening or a change in the shape of existing pigmented spots. As the tumor grows, it may cause visible masses on the iris, distortion of the pupil, or signs of inflammation such as redness or discomfort.
Signs of an oral melanoma often become noticeable when the tumor is large enough to interfere with normal functions. Owners may observe difficulty eating, excessive drooling, or an unusual odor from the mouth, often referred to as halitosis. Bleeding or the presence of a dark, raised, or cauliflower-like mass on the gums or tongue warrants immediate veterinary attention.
Cutaneous melanomas typically present as single, raised, firm masses on the skin, which may or may not be pigmented (darkly colored). While most skin masses are benign, an ulcerated or rapidly growing skin mass is a concerning sign of malignancy. Any new lump, discoloration, or a change in the size or shape of an existing pigmented spot should be assessed by a veterinarian.
Veterinary Diagnosis and Staging
A definitive diagnosis of melanoma requires a microscopic examination of the tissue, obtained through either a fine needle aspiration (FNA) or a biopsy. While FNA can sometimes suggest a melanocytic tumor, a surgical biopsy provides a larger tissue sample for histopathology. Histopathology is necessary to definitively determine if the tumor is benign or malignant, differentiating a benign melanocytoma from a malignant melanoma.
Once a malignant tumor is confirmed, the veterinarian will recommend cancer staging to determine if the disease has spread to other parts of the body. Staging typically involves three-view chest X-rays to check the lungs, abdominal ultrasound to examine the liver and other organs, and sampling of local lymph nodes. The results of these diagnostic tests are fundamental for predicting the cat’s prognosis and formulating an effective treatment plan.
The staging process helps establish the extent of the cancer’s spread, which is a significant factor in predicting the outcome. For example, the presence of cancer cells in regional lymph nodes or evidence of spread to the lungs or liver indicates a more advanced stage of disease. This information guides the oncology team in deciding whether local treatment alone is appropriate or if systemic therapy is required.
Management and Outlook for Cats
The primary treatment for localized feline melanoma is surgical excision, aiming to remove the entire tumor with clean margins. Clean margins mean surrounding healthy tissue is also removed to ensure no cancer cells remain. For ocular melanomas, if the tumor is large or causing secondary complications such as glaucoma, removal of the affected eye (enucleation) is often necessary to prevent pain and stop the spread of the disease. Cats generally adapt well to the loss of an eye and maintain a good quality of life.
When complete surgical removal is challenging due to the tumor’s location or if the tumor is aggressive, adjunctive therapies may be employed. Radiation therapy is effective for local control, especially for tumors that cannot be fully excised, like some oral melanomas. Chemotherapy or immunotherapy, such as a melanoma vaccine developed for dogs and sometimes used off-label in cats, may be considered for malignant tumors with metastasis risk.
The outlook for a cat with melanoma is strongly linked to the tumor’s location and its classification as benign or malignant. Benign melanomas, such as most cutaneous melanocytomas, are cured with successful surgical removal. Malignant oral and subungual melanomas carry a guarded to poor prognosis due to their aggressive nature and risk of spreading to the lungs and other organs. Early detection and aggressive treatment are the best approach to maximize survival time and maintain a high quality of life.