The behaviour of malignant tumours varies considerably. Not all spread easily to distant sites, although they can invade surrounding tissue. Injection-site sarcoma, for example, often causes problems through local growth, while different forms of lymphoma progress at different rates. The word cancer alone therefore does not establish an individual cat's prognosis.
When to see a vet urgently
A cat with cancer or suspected cancer needs urgent assessment if their condition clearly worsens:
- breathing is laboured or your cat breathes with an open mouth;
- mouth pain prevents eating or drinking;
- your cat is clearly distressed and prescribed pain relief is not helping.
You can find a vet near you.
Overview
Tumours can develop from any tissue in the body, including skin, lymphatic tissue, the digestive tract, bones or internal organs. The most common cancer types in cats include:
- lymphoma;
- carcinoma, such as squamous cell carcinoma and adenocarcinoma;
- sarcomas, including fibrosarcomas following vaccination;
- melanomas;
- mammary tumours.
The last entry refers to tumours of the mammary, or milk-producing, glands. Different tumour types are not equally common. Lymphoma is an important cancer group in cats and now often occurs in the digestive tract. A mammary tumour, meanwhile, may start as a small, firm lump beside a nipple. This kind of change needs investigation even if your cat otherwise seems lively.
Some sarcomas are associated with a previous injection site, but the description following vaccination does not cover every case. Similar tumours may arise in connection with other injections too. An injection-site sarcoma's local invasion of tissue affects how the first operation is planned. It is not treated like a superficial lump that separates easily.
Cancer often develops quietly, with the first signs frequently appearing at a late stage, making early diagnosis very important.
Causes
The reasons cancer develops in cats are not always precisely understood, but risk factors include:
- genetic predisposition;
- age, with older animals affected more often;
- chronic inflammation;
- viral infections, including feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV);
- carcinogens, such as tobacco smoke and chemicals;
- hormonal factors, particularly for mammary tumours.
Risk factors relate to particular cancer types rather than affecting every malignant tumour in the same way. FeLV infection is associated particularly with certain forms of lymphoma, but intestinal lymphoma can also develop without a diagnosed FeLV infection. Hormone exposure matters for mammary tumours, and not all the same environmental factors implicated in other cancers have been established as their causes.
Risk factors
Malignant tumours occur more often in cats that:
- are over 10 years old;
- are unvaccinated, in relation to FeLV and lymphoma risk;
- are unspayed females, in relation to mammary tumour risk;
- belong to certain breeds, with Siamese cats more susceptible to lymphomas and adenocarcinomas;
- have chronic inflammation.
More is known about risks for individual cancer types than about a risk profile shared by all feline cancers. The list does not mean that a young, neutered or vaccinated cat is protected against cancer. FeLV vaccination targets prevention of a viral infection and is not a general lymphoma vaccine. Siamese cats have also been reported to have a higher risk of mammary cancer, but breed alone does not determine a diagnosis.
Main symptoms
Symptoms depend on the tumour's type and location, but the most common include:
- lumps or swellings;
- wounds that fail to heal for a long time;
- loss of appetite and weight;
- listlessness and reduced activity;
- lameness or pain during movement;
- vomiting, diarrhoea or difficulty breathing with internal organ tumours;
- enlarged lymph nodes.
A tumour in an internal organ cannot always be felt from outside. Intestinal lymphoma may cause weight loss, vomiting or diarrhoea, and appetite may fall or sometimes increase. Palpation findings may be normal. The symptoms resemble many other intestinal diseases, so they cannot establish whether cancer is present.
Few symptoms can also be misleading. A small mammary lump may warrant investigation before ulceration or a deterioration in general condition develops. Equally, an enlarged lymph node does not itself indicate metastasis: inflammation may be responsible. Conversely, a normal-sized lymph node may contain tumour cells.
Complications and consequences
Without treatment, malignant tumours lead to:
- destruction of tissues and organs;
- bleeding and ulceration;
- metastatic spread to the lungs, liver, brain or bones;
- pain;
- wasting of the body, known as cachexia;
- death.
The list describes possible consequences rather than an inevitable sequence for every tumour. Local tissue damage and distant spread are assessed separately. Small-cell intestinal lymphoma, for example, may progress more slowly than the large-cell form and respond to treatment for a long time. The value of treatment is therefore not assessed solely on whether a tumour is labelled malignant.
Diagnosis at the vet
Investigations used to make a diagnosis include:
- a clinical examination and palpation;
- biopsy and histological examination, the gold standard;
- blood tests, including a complete blood count and biochemistry;
- ultrasound and X-rays to look for tumours and metastatic spread;
- CT or MRI to establish the location more precisely.
What do sampling and staging tell you?
Fine-needle sampling collects cells for microscopic examination. For some tumours, this may be enough for a diagnosis. A tissue sample also shows tissue structure and may provide information about tumour differentiation and invasion of surrounding areas. The sampling method is chosen according to the suspected tumour and possible surgery.
Stage describes where the tumour is and whether it has spread to nearby lymph nodes or more distant sites. Grade, meanwhile, describes microscopic characteristics and the behaviour predicted from them. They are not the same thing. Blood tests also assess your cat's other health conditions and fitness for treatment; normal blood results do not rule out intestinal lymphoma, for example.
Choosing treatment
Surgery, radiotherapy and cancer medication may be used alone or together. The plan is influenced by tumour type, location, extent of spread and your cat's other diseases. The aim is also agreed before treatment: complete removal, disease control or primarily relief of symptoms. Treatment options can be discussed with a vet experienced in oncology.
Surgery for a localised mammary tumour may mean removing more mammary tissue than the individual lump. Lymphoma treatment, by contrast, often relies on medication because the disease can affect several tissues. Surgery for an injection-site sarcoma may be supplemented with radiotherapy. Treatment given to another cat for a similar-looking lump may therefore be unsuitable for your cat.
Monitoring of the surgical site continues after removal of an injection-site sarcoma. The tumour can return even when the margins of the removed tissue were assessed as clean. Tell the treating vet if a new lump appears around the scar or a previous change starts growing. Recurrence affects planning of further treatment.
During chemotherapy, both disease response and adverse effects are monitored. Maintaining good quality of life is a central aim in animal treatment, and many cats tolerate medication well. Possible adverse effects include loss of appetite, vomiting and a fall in white blood cell numbers. Monitoring may therefore require blood tests and treatment adjustments. Do not alter medication yourself.
Daily life and symptom relief
Monitor eating, weight, drinking, movement and whether your cat can reach their usual resting places. A mouth tumour can make picking up food difficult, while intestinal disease can impair nutrient use. If eating decreases, the vet assesses the cause and any need for a dietary change or other support. Repeatedly offering food alone does not correct pain or nausea.
Bring the litter tray and other essentials closer for a cat with poor mobility. If grooming decreases, the coat can be cared for gently. Appropriate pain relief and sufficient fluid intake belong in the care plan even when the tumour cannot be cured. Palliative care, which relieves symptoms, can continue alongside other cancer treatment.
Agree in advance whom to contact if breathing changes or pain worsens. If suffering cannot be controlled, discuss end-of-life care and the timing of euthanasia with your vet. The decision considers your cat's condition and the benefit of treatment, rather than tumour size alone.
Prevention
Cancer cannot be prevented completely, but the risk may be reduced through:
- FeLV vaccination;
- spaying female cats before their first season, reducing mammary tumour risk by 90%;
- avoiding smoking at home;
- a good-quality diet and weight monitoring;
- regular veterinary check-ups, particularly for older cats.
The 90% risk reduction mentioned is an approximate research estimate for mammary tumours in cats spayed early. It does not mean equivalent protection against every cancer or guarantee that a mammary tumour cannot develop. The timing of spaying affects the reduction in risk. The need for FeLV vaccination and other preventive care is planned according to your cat's infection risk.
What it means for owners
Malignant tumours are among the most common causes of death in older cats. Owners should remember that early detection of lumps and unusual symptoms offers an opportunity for effective treatment. Regular checks and close attention to your pet's health may extend their life.
Frequently asked questions
Can you tell whether a lump is malignant?
Not reliably from size, softness or feeling it alone. A cell or tissue sample helps establish the type of change. Even a mass seen on imaging often needs sampling so that treatment can be planned.
Does a cancer diagnosis mean my cat can no longer be helped?
No. Some tumours can be treated locally, while others can be controlled with medication. If a cure is not possible, pain and other symptoms can still be relieved. Discuss the prognosis according to the specific tumour type identified and your cat's condition.
Are blood tests enough to screen for cancer?
They provide useful health information, but normal results do not rule out every cancer. With intestinal lymphoma, for example, blood values and sometimes even ultrasound can be normal. Persistent symptoms are therefore investigated with other tests when needed.
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
- 2026 AAHA Oncology Guidelines for Dogs and Cats, American Animal Hospital Association, accessed 2026-11-02.
- Mammary Tumours, Cornell University College of Veterinary Medicine, accessed 2026-11-02.
- Lymphoma, Cornell University College of Veterinary Medicine, accessed 2026-11-02.
- Home Care for the Cancer Patient, Cornell University College of Veterinary Medicine, accessed 2026-11-02.
- Mammary Tumours in Cats, Merck Veterinary Manual, accessed 2026-11-02.
- Medical Oncology: Feline Injection Site Sarcoma, North Carolina State University, accessed 2026-11-02.
- Section 3: Tumour Diagnostics & Staging, American Animal Hospital Association, accessed 2026-11-02.
- Section 5: Therapeutic Interventions, American Animal Hospital Association, accessed 2026-11-02.