A basal cell tumour may be benign, whereas basal cell carcinoma means the malignant form. The term basalioma alone is not enough to assess how a cat's tumour will behave. The course of mast cell tumours also varies. A sample establishes the precise tumour type, and the changes mentioned above should not all be regarded as equally dangerous.
When to see a vet urgently
Contact a vet promptly if a skin lesion is accompanied by any of the following signs:
- heavy or persistent bleeding;
- severe pain or a lesion that prevents eating or normal movement;
- an ulcerated tumour together with a clear deterioration in general condition;
- failure to eat and weight loss associated with a lesion around the mouth or muzzle.
You can find a vet near you.
Overview
Skin tumours differ in their origins and clinical course. Benign tumours grow slowly and are not generally associated with metastasis, while malignant tumours can spread to other organs and threaten life. Owners often discover a cat's tumours while stroking or grooming them, so regular checks are very important.
By definition, a benign tumour does not spread to distant sites. It can still trouble your cat because of its size, location or ulceration. Malignancy, meanwhile, can involve aggressive invasion of local tissue, the possibility of distant spread, or both. A tumour's size or rounded shape does not distinguish these possibilities on its own.
Causes
The precise causes of skin tumours are not fully understood, but risk factors include:
- Genetic predisposition.
- Exposure to UV radiation, particularly in white cats.
- Chronic skin problems and inflammation.
- Viral infections, such as feline papillomavirus.
- Immune system disorders.
- Age-related changes.
Risk factors
Skin tumours occur more often in:
- Older cats.
- White cats, particularly in relation to the risk of basal cell carcinoma.
- Cats with chronic skin inflammation or injuries.
- Certain breeds, such as Siamese, Persian and Maine Coon cats, according to studies.
Risk factors depend on the tumour type, and the whole list cannot be applied to every skin tumour. The link between pale or white skin and sunlight is recognised particularly for squamous cell carcinoma, rather than as a general feature of basal cell carcinoma. A lesion often starts in a sparsely haired area, such as an ear tip, the nose or an eyelid.
UV radiation from sunlight can damage the genetic material in skin cells. Not all skin cancers are related to sunlight, however, and a dark-coated cat can also have a malignant skin lesion. Breed or coat colour does not replace investigating a lump. General tumour risk lists always need to be supplemented by information about the tumour type suspected.
Main symptoms
The symptoms of skin tumours depend on the type of tumour:
- Lumps or patches on the skin.
- Firm areas in the tissue beneath the skin.
- Wounds that do not heal well.
- Hair loss over the tumour.
- Itching or pain.
- Enlarged lymph nodes with malignant tumours.
An early skin lesion caused by squamous cell carcinoma may look like a small scab or scratch. It may seem to heal at times and later return in the same place. A recurring scabby area therefore deserves investigation even if it does not form an obvious rounded lump. As it progresses, the lesion may ulcerate and damage surrounding tissue.
A skin tumour can look like inflammation, while an inflamed-looking area may contain a tumour. Hair loss, redness or discharge therefore does not establish the diagnosis alone. Tell your vet when the change was first noticed and how it has developed. Also mention any lump previously removed from the same site.
Complications and consequences
Malignant skin tumours can lead to:
- Metastases in the lungs, liver and lymph nodes.
- Chronic pain.
- Bleeding and wound infections.
- Deterioration in general condition and death.
Diagnosis at the vet
Investigations used to reach a precise diagnosis include:
- A clinical examination.
- Cytology (fine-needle sampling).
- Biopsy and histological examination, the gold standard.
- Blood tests and ultrasound to look for spread in malignant tumours.
Cytology means examining individual cells under a microscope. A fine-needle sample collects cells from a lump using a thin needle; it does not involve giving fluid into the tissue. Some tumours yield a readily identifiable cell pattern this way. Others shed too few cells, so a scant sample does not rule out a tumour.
Histology examines tissue structure in a biopsy or removed tumour. The sample provides more information about how cells are arranged and invade their surroundings. If a larger biopsy is needed, its site is planned with a possible definitive operation in mind. A lump is therefore not always removed immediately without an investigation plan.
Investigations may also include staging, or assessing the extent of disease. The aim is to find out whether changes elsewhere in the body affect treatment choices. The imaging and lymph node samples needed depend on the tumour type. Blood tests help assess general health, but a normal result alone does not rule out a local skin tumour.
A lump at an injection site
An injection-site sarcoma is a tumour arising from connective tissue that can grow deep into surrounding tissues. It differs from short-lived swelling after an injection. Tell the vet whether a vaccination or another injection was given in the same area. An injection history does not, however, establish the nature of a lump on its own.
A mass at an injection site needs consideration for sampling if it persists for three months, is more than two centimetres wide or continues growing one month after the injection. These are specific criteria for assessing injection-site lumps. They are not a reason to delay investigating another suspicious or rapidly changing skin lesion.
If an injection-site sarcoma is suspected, CT or MRI may help establish the extent of the lesion before surgery. Chest imaging looks for signs of spread, and regional lymph nodes may be examined with cell samples. This information affects planning the procedure.
Treatment and follow-up
Surgery is a main treatment for many skin tumours. Removing a malignant tumour often requires removing surrounding healthy tissue too, because the visible boundary may not reflect the extent of microscopic growth. Planning the first operation is particularly important for tumours that invade tissues. The treating vet may consider specialist surgical or oncology expertise necessary.
The removed tumour is sent for histological examination. The report may also describe the surgical margins, meaning the edges of the removed tissue. If tumour cells extend to the edge, some may remain in your cat's body. A clean margin, meanwhile, means no tumour is seen at the examined edges. The need for further treatment is assessed according to the report and tumour type.
Radiotherapy can help control local disease, for example when a tumour cannot be removed completely. Chemotherapy is considered for some malignant tumours. Freezing treatment may also suit small, superficial lesions. Not every method suits every tumour, and the treatment plan takes its location and your cat's other health conditions into account.
Particular features of mast cell tumours
A skin mast cell tumour in a cat often occurs around the head or neck. Its behaviour may differ from mast cell tumours in dogs, so experience of treating a dog does not directly establish a cat's prognosis. A cell sample is often useful for identification. In some cats the skin lesion is localised, but the need for staging investigations is still assessed individually.
Mast cell tumours may release histamine and other inflammatory mediators. The vet may therefore plan other medication around handling the tumour and surgery. Do not start these products at home on your own initiative. Histology and any additional findings influence whether further treatment is needed after removal.
Monitoring after treatment
Check the surgical site as instructed and report a new lump or wound change. Local recurrence and metastases are different: a tumour can return at the surgical site without identified spread to distant areas. Follow-up investigations are chosen according to the risks associated with the original tumour. The rest of the skin is also checked for new changes.
Prevention
There is no specific way to prevent skin tumours, but the risk may be reduced by:
- Limiting time in the sun for white cats.
- Treating chronic skin inflammation promptly.
- Checking your cat regularly and seeking veterinary attention as soon as a lump or sore is found.
- Supporting immune function with a balanced diet.
Avoiding sunlight is most useful for protecting pale, sparsely haired skin against sun-related squamous cell carcinoma. It does not prevent every skin tumour. During checks at home, look for recurring scabby areas on the nose and ears as well as lumps. Balanced feeding supports general health but cannot guarantee that tumours will be prevented.
Important for cat owners
Skin tumours are common in cats, and not all are dangerous. However, owners should remember that a new growth always needs a veterinary examination. Only a biopsy can confirm whether a tumour is benign or malignant. Early detection greatly improves the chances of successful treatment.
A cell sample can provide a very reliable identification for some tumour types, but a tissue sample is often needed for a more detailed assessment of structure and malignancy. Your vet will explain whether the first sample is enough or a biopsy is required. Monitoring a lump without treatment is considered only after its nature and possible effects have been assessed.
This material provides information and does not replace treatment advice. Contact a vet as soon as the first signs of illness appear.
Frequently asked questions
Can a small skin lump be malignant?
Yes. An early malignant tumour can also feel small and well-defined. Appearance or size does not replace examining cells or tissue. Show any new or changing lump to your vet.
Do all benign skin tumours need removing?
Not necessarily. If the lesion has been investigated, does not ulcerate and does not interfere with your cat's activities, monitoring may be appropriate. However, problems caused by growth, pain or location may favour removal even for a benign tumour.
Why is a tumour examined after it is removed?
Histology confirms the tumour type and may provide information about its behaviour and the surgical margins. The result helps guide further treatment and monitoring. Removing the visible lump alone does not provide all this information.
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
- Tumours of the Skin in Cats, Merck Veterinary Manual, accessed 2026-11-02.
- Overview of Tumours of the Skin and Soft Tissues in Animals, Merck Veterinary Manual, accessed 2026-11-02.
- Mast Cell Tumours, American College of Veterinary Surgeons, accessed 2026-11-02.
- Medical Oncology: Feline Injection Site Sarcoma, North Carolina State University, accessed 2026-11-02.
- Squamous Cell Cancer: Dangerous, Cornell Feline Health Centre, accessed 2026-11-02.