Cancer in Cats: Recognising the Signs and What to Expect

Cancer is less common in cats than in dogs, but when it does occur it tends to be more aggressive and harder to detect early. Cats are masters at concealing illness — an evolutionary survival instinct that unfortunately means many feline cancers are not diagnosed until they have reached an advanced stage. Approximately one in five cats will develop cancer during their lifetime, with risk increasing significantly after the age of ten.

"Cats hide pain and illness better than almost any species I work with. By the time a cat owner notices something is wrong, the cancer has often been developing for weeks or months. This is why I always encourage cat owners to maintain regular veterinary visits — even for indoor cats who seem perfectly healthy." — Dr. Sarah Chen, DVM

Unlike dogs, where certain breeds have well-documented cancer predispositions, feline cancer risk is more closely linked to viral status, particularly feline leukaemia virus (FeLV) and feline immunodeficiency virus (FIV). Cats positive for either virus face a significantly elevated cancer risk, which is one of many reasons why vaccination and testing are so important.

Indoor cats are not immune to cancer. While outdoor cats face additional risks such as UV exposure (linked to squamous cell carcinoma), the most common feline cancers — lymphoma and mammary cancer — occur regardless of lifestyle. Understanding what to look for gives you the best chance of catching cancer early, when treatment is most effective.

Detecting cancer in cats is challenging because cats instinctively mask illness. However, there are several key changes that should prompt a veterinary visit. Any one of these signs persisting for more than a few days warrants investigation.

Behavioural Changes

• Increased hiding — a cat that suddenly spends more time under beds, in cupboards, or in secluded areas may be experiencing pain or feeling unwell. This is one of the earliest and most commonly missed signs of pain in cats
• Lethargy and withdrawal — reduced interest in play, interaction, or grooming. Cats that stop grooming often develop an unkempt, matted coat
• Changes in vocalisation — increased meowing, yowling, or growling can indicate discomfort

Physical Signs

• Unexplained weight loss — one of the most significant warning signs. Even a loss of 300–500 grams in a cat is proportionally significant and should not be ignored
• Lumps and bumps — any new lump should be examined, particularly along the mammary chain (underside of the belly). In cats, approximately 85% of mammary tumours are malignant
• Oral lesions — sores, swelling, bleeding, or foul odour from the mouth may indicate squamous cell carcinoma, the most common oral cancer in cats
• Breathing changes — rapid breathing, open-mouth breathing, or laboured respiration can indicate a chest mass (mediastinal lymphoma) or fluid accumulation around the lungs
• Nasal discharge — persistent discharge, particularly if bloody or from one nostril, may indicate nasal lymphoma or carcinoma

Digestive Symptoms

• Chronic vomiting or diarrhoea — gastrointestinal lymphoma, the most common form of feline lymphoma, often presents with persistent vomiting, diarrhoea, and weight loss
• Loss of appetite — anorexia lasting more than 24–48 hours in a cat is always cause for concern and can be dangerous on its own, as cats are prone to hepatic lipidosis (fatty liver disease) when they stop eating

Indoor cats benefit from owners who are attuned to subtle changes. Keeping your cat at a healthy weight and mentally stimulated also makes it easier to notice when something has changed.

Several cancer types predominate in cats, each with distinct presentations and behaviours. Understanding these helps owners recognise potential symptoms and have more informed conversations with their veterinary team.

Lymphoma

Lymphoma is by far the most common cancer in cats, accounting for approximately 30% of all feline tumours. It arises from lymphocytes and can affect virtually any organ. The gastrointestinal (GI) form is most common in older cats, presenting with vomiting, diarrhoea, and weight loss. Mediastinal lymphoma (affecting the chest) is more common in younger cats and is strongly associated with FeLV infection. Renal lymphoma affects the kidneys and can cause increased drinking and urination, while nasal lymphoma presents with nasal discharge and sneezing.

Squamous Cell Carcinoma (SCC)

Squamous cell carcinoma is the second most common cancer in cats and can occur in two primary locations. Oral SCC is a highly aggressive tumour that affects the tongue, gums, or palate, causing difficulty eating, drooling, and weight loss. Cutaneous SCC affects the skin, particularly on the ear tips, nose, and eyelids of white or light-coloured cats — UV exposure is a significant risk factor. Keeping cats indoors reduces skin SCC risk substantially.

Fibrosarcoma (Injection-Site Sarcoma)

Fibrosarcomas are malignant tumours of connective tissue. A particular form — injection-site sarcoma — develops at the location of previous vaccinations or injections. While rare (occurring in approximately 1 in 10,000 to 1 in 30,000 vaccinations), these tumours are locally aggressive and difficult to treat. This is why veterinary protocols now recommend specific injection sites on the limbs rather than between the shoulder blades, and why vaccination schedules should follow evidence-based guidelines.

Mammary Cancer

Mammary tumours are the third most common cancer in female cats, and unlike dogs where roughly half of mammary tumours are benign, approximately 85–90% of feline mammary tumours are malignant. Siamese cats may have a higher incidence. Spaying before six months of age reduces mammary cancer risk by approximately 91%, while spaying before one year reduces risk by about 86%. Intact or late-spayed female cats are at the highest risk.

Feline leukaemia virus (FeLV) is one of the most important risk factors for cancer in cats. FeLV-positive cats are approximately six times more likely to develop lymphoma than FeLV-negative cats. The virus integrates its genetic material into the cat's cells, disrupting normal cell growth regulation and leading to uncontrolled proliferation — the hallmark of cancer.

FeLV is transmitted through close contact — mutual grooming, shared food and water bowls, and bite wounds. Kittens are most susceptible, particularly through in-utero transmission from an infected mother. While many cats can fight off FeLV exposure, those who become persistently infected carry the virus for life and face ongoing cancer risk.

How FeLV Leads to Cancer

The virus can cause cancer through several mechanisms. It may insert itself near oncogenes (genes that promote cell growth), effectively switching them on. It can also suppress the immune system, reducing the body's ability to identify and destroy abnormal cells before they become cancerous. FeLV-associated lymphomas tend to occur in younger cats (often under five years old) and are frequently mediastinal in form, causing breathing difficulty and fluid accumulation in the chest.

Prevention Is Key

FeLV vaccination is highly effective and is recommended for all kittens and at-risk adult cats. Testing is recommended before vaccination and whenever a new cat enters the household. Keeping cats indoors and preventing contact with cats of unknown FeLV status dramatically reduces transmission risk. For a detailed breakdown of feline vaccination schedules, see our cat vaccination guide.

Feline immunodeficiency virus (FIV) also increases cancer risk, though to a lesser degree than FeLV. FIV-positive cats have approximately twice the lymphoma risk of FIV-negative cats. Both viruses suppress immune function, making regular veterinary monitoring essential for infected cats.

Diagnosing cancer in cats follows a similar process to dogs but requires particular sensitivity to feline stress and handling. Many diagnostic procedures can be performed with minimal sedation, and your veterinary team will prioritise your cat's comfort throughout the process.

Initial Assessment

Your vet will begin with a thorough physical examination, palpating the abdomen for masses, checking all lymph node stations, examining the mouth, and assessing body condition. Blood work including a complete blood count, biochemistry panel, and FeLV/FIV testing provides essential baseline information. Weight history is particularly important — even small losses can be diagnostically significant in cats.

Imaging

Abdominal ultrasound is one of the most valuable diagnostic tools for feline cancer, particularly for GI lymphoma. It can reveal thickened intestinal walls, enlarged mesenteric lymph nodes, and masses in organs. Chest X-rays assess the lungs and mediastinum. Advanced imaging such as CT scans may be recommended for surgical planning or to evaluate complex cases.

Tissue Diagnosis

Fine needle aspirates can provide rapid initial information, but many feline cancers require biopsy for a definitive diagnosis. For GI lymphoma, endoscopic biopsies or full-thickness surgical biopsies of the intestinal wall are often necessary. Immunohistochemistry — a laboratory technique that identifies specific proteins on cancer cells — is particularly important in cats, as it distinguishes B-cell from T-cell lymphoma, which has significant prognostic and treatment implications.

Staging

Once cancer is confirmed, staging determines how far it has spread. This typically includes imaging of the chest and abdomen, bone marrow aspirate (for lymphoma), and examination of multiple lymph node stations. Staging is essential for determining prognosis and selecting the most appropriate treatment protocol.

Treatment for feline cancer has advanced significantly, and many cats tolerate therapy well with good quality of life during treatment. The approach depends on the cancer type, stage, your cat's overall health, and your family's goals.

Surgery

Surgical removal remains the treatment of choice for localised solid tumours. Mammary tumours typically require radical mastectomy (removal of the entire mammary chain) because of the high malignancy rate. Fibrosarcomas require wide surgical margins — often 3–5 centimetres in all directions — which can make removal challenging. For oral SCC, surgery is often limited by the tumour's location and extent.

Chemotherapy

Cats generally tolerate chemotherapy better than many owners expect. For lymphoma, common protocols include COP (cyclophosphamide, vincristine, prednisolone) and modified Wisconsin-Madison protocols. Side effects are typically mild — approximately 80% of cats experience no significant adverse effects. Treatment is administered at weekly or biweekly intervals, and most cats continue their normal routines between appointments.

Radiation Therapy

Radiation is particularly effective for nasal lymphoma and tumours that cannot be completely excised surgically. It requires specialised facilities and involves multiple sessions under brief anaesthesia. Most cats tolerate radiation well, though localised skin irritation and temporary hair loss in the treatment area are common.

Prognosis by Cancer Type

Prognosis varies enormously. Low-grade GI lymphoma in cats can respond exceptionally well to oral chemotherapy (chlorambucil and prednisolone), with median survival times of two to three years. High-grade lymphoma treated with chemotherapy has a median survival of six to nine months. Mammary cancer prognosis depends on tumour size and whether it has spread — early detection and complete surgical removal offer the best outcomes. Oral SCC unfortunately carries a poor prognosis regardless of treatment, with median survival times of two to four months.

Quality of life should always guide treatment decisions. Your veterinary team can help you assess whether treatment is improving your cat's comfort and wellbeing, and palliative care is a compassionate option when curative treatment is no longer appropriate.