A benign melanocytic tumour is more precisely called a melanocytoma. Melanoma usually means a malignant tumour. Dark colour alone cannot distinguish the two, and a pale tumour does not rule out melanoma.
When to see a vet urgently
Seek urgent assessment if your cat develops any of the following:
- squinting, redness and obvious eye pain, or sudden deterioration in sight;
- bleeding from the mouth that does not stop, or difficulty eating and swallowing;
- breathing difficulty, collapse or rapidly worsening general health.
Overview
Melanoma appears as a dark, black or brown lump or patch, but non-pigmented, or amelanotic, forms also occur. The tumour can ulcerate, grow and spread to regional lymph nodes and the lungs. Iris melanoma is the most common form in cats. Oral melanomas are less common but are very aggressive and have a poor prognosis.
The iris is the coloured part of the eye surrounding the pupil. Iris melanoma is the most common primary tumour developing inside a cat's eye. Melanosis, which can look similar, means benign proliferation of pigment cells. It may be impossible to distinguish melanosis from early melanoma by appearance. Not all pigment changes become cancerous, but the course of an individual change cannot be predicted reliably.
Causes
The exact causes are not fully understood, but possible factors include:
- an inherited predisposition;
- chronic inflammation of the skin or mucous membranes;
- excessive sunlight in skin forms;
- age, with older cats affected more often;
- immune system disorders.
These possibilities should not be interpreted as proven causes of feline melanoma. In cats, sunlight is more clearly associated with squamous cell carcinoma of the skin, a different cancer. Feline melanoma has little association with sun damage compared with human melanoma. Inflammation, genetics or an immune system change also cannot usually be established as the cause in an individual cat.
Risk factors
- Older cats, over 10 years of age.
- Cats with chronic inflammatory diseases of the mouth.
- Cats with dark fur and skin, more often with skin forms.
- Certain breeds, such as Siamese and Orientals, may be more susceptible.
There is little research on risk factors for melanoma in cats. No confirmed breed predisposition has been established, and dark fur, the breeds mentioned or oral inflammation cannot be used as reliable measures of risk. Older cats are typical patients, but the age threshold does not exclude younger cats from investigation.
Typical symptoms
Skin melanoma:
- a pigmented, dark patch or lump on the skin;
- gradual enlargement of the tumour;
- ulceration and hair loss over the tumour.
Even a small or intact skin lump should be shown to a vet: appearance cannot reliably predict tumour cell behaviour. A melanocytic skin tumour may be solitary, or several changes may be present. Monitoring size and ulceration provides information about progression, but does not replace sampling.
Oral melanoma:
- a tumour on the gums, tongue or lining of the mouth;
- bad breath;
- bleeding and difficulty chewing;
- reduced appetite and weight loss.
Oral pain may show as dropping food or reluctance to chew. The local extent of an oral tumour determines how readily it can be removed and how well the cat can eat afterwards. However, pigment or breath odour alone cannot identify the tumour type.
Eye melanoma:
- dark patches or lumps in the eye;
- changes in iris colour;
- glaucoma and deteriorating sight.
Photographing an eye change under the same lighting can be useful. Concerning findings include a raised pigmented area, thickening of the iris and a change in pupil shape. Photographs help compare changes, but cannot assess raised eye pressure or deeper tissue growth. Normal eye pressure does not rule out melanoma either. At follow-up, new findings are compared with previous photographs and examination results.
Complications and consequences
- rapid spread to lymph nodes and lungs;
- destruction of tissue in the mouth, eyes or skin;
- chronic pain and wasting;
- death in untreated malignant forms.
The possibility of spread does not mean metastases are present in every cat at diagnosis. A tumour inside the eye can also obstruct normal drainage of fluid. Pressure then rises, causing painful glaucoma. Pain must be treated even while the extent of the tumour is still being investigated.
Diagnosis at the vet
- clinical examination of the tumour;
- cytology, which is not always reliable because cells may resemble one another;
- biopsy and tissue examination, the main diagnostic method;
- chest X-rays and abdominal ultrasound to look for spread;
- an eye examination for an ocular form.
A cell sample is taken with a fine needle, while a tissue sample also shows how cells are arranged and how they grow into surrounding tissue. If cells contain little pigment, the pathology laboratory may need additional stains to identify their origin. Where possible, the edges of a removed tumour are also examined to see whether tumour cells remain at the surgical margins.
Staging investigations are chosen according to tumour location, findings and planned treatment. Lymph nodes may be sampled, and the chest or abdomen imaged. Normal imaging does not rule out microscopic metastases. Nevertheless, not every possible investigation is performed automatically in every patient.
An eye examination assesses the iris surface, pupil function, inflammation and eye pressure, among other things. An iris biopsy is possible in some situations, but carries a risk of inflammation and bleeding. A small sample may also come from an area without malignant cells. A benign sample result therefore does not always settle the condition of the whole eye. Tissue examination of a removed eye often provides the final diagnosis.
Treatment
Treatment of a localised tumour often relies on surgery. For skin and oral changes, removal depends on whether enough healthy tissue around the tumour can be removed without unacceptably impairing the cat's function. Sampling and surgery should be planned together so that the first procedure supports any further treatment.
Eye removal is considered if the tumour seems to be progressing or the eye is painful and blind. In an eye that can see, the possibility of a benign pigment change is also weighed. The decision is made with a vet experienced in eye disease: a new brown spot alone is not a decision to remove the eye.
Radiotherapy or medical cancer treatment may be considered individually. However, far less is known about outcomes in cats than dogs. Information has been published on the safety in cats of a melanoma vaccine developed for dogs, but this does not demonstrate improved survival in cats. It is also not a routine preventive vaccine for a healthy cat.
At home, monitor eating, swallowing, weight trends, rest and willingness to join familiar activities. Pain, nausea or difficulty using the mouth can reduce appetite and should be reported to the vet treating your cat. Do not force food into the mouth. Nutritional support and symptom relief are planned separately where needed. Symptomatic care is also part of treatment when the tumour cannot be completely removed.
Losing an eye does not, on its own, mean poor quality of life. If sight is impaired, keep food, water and the litter tray in familiar places, avoid moving furniture and prevent falls on stairs. Speak as you approach so that touch does not startle your cat.
Prevention
- Check an older cat's skin and mucous membranes regularly.
- See a vet promptly if you find a pigmented or rapidly growing change.
- Exclude animals with an inherited predisposition from breeding.
- Protect white and pale-coloured cats from excessive sunlight.
No specific way to prevent melanoma or genetic test suitable for routine assessment of inherited risk has been established. Breeding decisions should therefore not be based solely on coat colour or a presumed breed predisposition. Sun protection is sensible, particularly to help prevent other tumours in pale skin, but cannot guarantee protection against melanoma.
Prognosis
The outlook is assessed according to tumour location, tissue examination, local growth and spread. Removal of a benign skin melanocytoma may be enough treatment. For a malignant tumour, successful surgery and any metastases change the situation. The prognosis for an eye pigment change cannot be determined from colour alone, and another cat's disease course does not predict your own cat's outcome.
Important for cat owners
Melanoma is rare in cats but can be extremely dangerous, particularly in the mouth and eyes. Remember that any pigmented patch or lump that grows or ulcerates needs prompt investigation, preferably by a vet experienced in cancer. Only biopsy and tissue examination can confirm the diagnosis. Skin melanoma found early can often be removed successfully, but the outlook for oral and eye forms is guarded or poor.
This article provides general information and does not replace veterinary care. If you notice signs of illness in your cat, contact a vet.
Frequently asked questions
Is a brown spot in a cat's eye always melanoma?
No. Benign melanosis can resemble early melanoma. Arrange an eye examination and follow the agreed monitoring plan. A growing or raised change, an abnormal pupil or eye pain needs reassessment.
Can melanoma be pale?
Yes. An amelanotic tumour contains little visible pigment and may resemble another tumour type. Identification relies on samples and, where necessary, additional stains, rather than whether a lump is black.
Can an eye biopsy always avoid removal of the eye?
No. A biopsy suits some situations, but the small sample size and sampling site affect interpretation. The decision also considers vision, pain, progression of the change and examination findings.
This article is for general information only and is not a guide to treatment. If you notice the first signs of illness, contact your vet.
Paw4care editorial team
Sources
- Melanoma of the dog and cat: consensus and guidelines, Frontiers in Veterinary Science, accessed 2026-11-03.
- Tumours of the Skin in Cats, Merck Veterinary Manual, accessed 2026-11-03.
- Feline Iris Hyperpigmentation, MSPCA-Angell, accessed 2026-11-03.
- Assessment of the diagnostic accuracy of clinical signs in feline diffuse iris melanoma, Frontiers in Veterinary Science, accessed 2026-11-03.
- Section 3: Tumour Diagnostics and Staging, AAHA, accessed 2026-11-03.
- 2023 AAFP/IAAHPC Feline Hospice and Palliative Care Guidelines, AAFP/IAAHPC, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Blind cats, Cats Protection, accessed 2026-11-03.
- Initial Triage and Resuscitation of Small Animal Emergency Patients, Merck Veterinary Manual, accessed 2026-11-03.
- Feline iris melanosis, Colorado State University, accessed 2026-11-03.