When to see a vet urgently
Weakening of bone or pain associated with a bone tumour may need urgent treatment:
- Your cat suddenly stops bearing weight on a limb or the limb looks out of alignment.
- Pain is severe and your cat refuses to move.
- Breathing becomes difficult or your cat breathes with an open mouth.
- Jaw swelling and pain prevent eating.
These signs do not prove a tumour, but their cause needs prompt investigation. You can find a vet near you.
Overview
Bone tumours arise from bone or cartilage cells. Benign tumours grow slowly and rarely metastasise but can change bone shape. Malignant tumours such as osteosarcoma aggressively destroy bone, cause severe pain and often spread to the lungs.
By definition, a benign tumour does not produce distant metastases. The reference to rare spread above therefore does not describe the usual behaviour of a genuinely benign tumour. Even a local lesion can still cause problems by compressing tissue or changing bone structure.
Malignant tumours also vary in behaviour. Feline osteosarcoma generally metastasises less often than its canine counterpart. The lungs are a possible site, but spread is not inevitable in every cat. Severe local bone destruction and distant spread are separate characteristics.
A tumour seen in bone may originate there or reach it from elsewhere. In the latter situation, it may be a metastasis or invasion from an adjacent soft tissue tumour. Establishing the distinction affects which other areas are examined and what treatment is possible.
Causes
The precise causes of bone tumours are not always known, but risk factors include:
- Genetic predisposition.
- Chronic inflammation and bone injuries.
- Previous radiotherapy.
- Viral diseases and cancer.
- Age-related changes.
Most primary bone tumours develop without a recognisable single cause. Tumours have been described at sites of old fractures, implants or radiotherapy, but such associations are rare. An ordinary healed fracture therefore does not mean your cat is likely to develop cancer.
The category of viral diseases and cancer is too broad to explain every bone tumour. Limited feline studies have not established a clear association between osteosarcoma and FIV or FeLV, for example. Different tumour types therefore need distinguishing when considering possible causes too.
Risk factors
Bone tumours are diagnosed more often in:
- Older cats.
- Animals with previous fractures or chronic bone inflammation.
- Cats with weakened immunity or cancer.
Information on feline risk factors is limited, and the list does not establish an independent effect for every factor. Bone tumours also occur without previous injury or impaired immune defences. A cat's symptoms should not go unassessed because they do not fit an assumed risk group.
Main symptoms
Symptoms depend on tumour location:
- Persistent lameness.
- Pain on palpation.
- Swelling and limb deformity.
- Pathological fractures under slight loads.
- Tiredness, reduced appetite and weight loss.
- Breathlessness with lung metastases.
With limb osteosarcoma, your cat may walk and play less because of pain. Local swelling may feel warm, but inflammation can cause the same finding. Palpation alone does not distinguish a tumour from other bone diseases.
A jaw tumour may draw attention through difficulty opening the mouth, drooling and reluctance to eat. Lesions in bones of the trunk do not always cause limb swelling. Location is therefore as important to the history as the severity of lameness. Difficulty breathing should not automatically be attributed to lung metastases, because other causes are possible.
Complications and consequences
Malignant bone tumours can lead to:
- Severe pain and lameness.
- Bone loss and fractures.
- Metastases in the lungs, liver and other organs.
- Severe intoxication and death.
A pathological fracture means bone weakened by disease breaks under less stress than usual. It may explain sudden deterioration in a cat already limping. Do not test a painful limb by encouraging weight-bearing to see whether your cat can still walk.
The word intoxication in the list does not mean poisoning by an external substance. A tumour can impair general condition and cause pain, tissue damage or widespread disease. Treatment needs and prognosis are determined by these actual findings.
Diagnosis at the vet
Investigations used to establish and confirm the diagnosis include:
- X-rays for bone changes.
- Computed tomography to assess tumour size and metastases.
- Biopsy and histology, the gold standard.
- Blood tests for anaemia, inflammation and biochemical changes.
- Chest X-rays to look for metastases.
X-rays may show bone destruction and new bone formation. An aggressive-looking lesion does not identify the tumour type on its own: bone inflammation can produce similar findings. Fine-needle samples examine collected cells but do not always provide a sufficient answer.
A biopsy assesses tissue structure and the nature of the tumour. The sampling site is planned so it can be removed during later surgery if needed. This avoids unnecessarily complicating definitive surgery. The sampling method is chosen according to bone strength and lesion location.
Staging looks for distant spread and assesses your cat's other health conditions before a treatment decision. Chest images help even when breathing is normal. The abdomen and abnormal lymph nodes are examined if needed. Normal blood tests alone do not rule out a bone tumour.
Computed tomography can define local extent more precisely, such as the tumour's relationship to adjacent bones and soft tissues. Surgical planning needs to establish how much tissue must be removed. The removed tumour is sent for histology to assess its type and, where appropriate, whether the margins are clear.
Treatment options
Surgical removal is an important treatment for a localised bone tumour. In a limb, this may mean amputation, or removal of the affected limb. This also removes a substantial source of pain and fracture-prone bone. For a head or trunk tumour, the possibility of surgery depends on the precise location and how extensively it can be removed.
Many cats adapt well to limb removal. Planning nevertheless assesses other health conditions, mobility and expected benefit individually. Effective pain relief is needed before and after surgery. Tell the vet if your cat remains withdrawn or avoids moving despite treatment.
Radiotherapy may be considered when a tumour cannot readily be removed, for example. Symptom-relieving care is also possible if treatment aimed at removal is unsuitable. Its purpose is to ease pain and maintain quality of life. Pain control is needed regardless of visible metastases.
Individual assessment of chemotherapy
Feline osteosarcoma has traditionally often been treated with surgery alone because metastases were considered much less common than in dogs. A more recent study of surgically treated cats found more spread than earlier reports. Adding chemotherapy was associated with longer survival in osteosarcoma patients without identified lung metastases before surgery.
This was a review of medical records rather than a randomised treatment trial. The finding nevertheless provides a reason to discuss the possible benefit of additional treatment with a vet experienced in oncology. The choice depends on tumour type, extent of spread and your cat's condition. Not every bone tumour has the same follow-up treatment.
Prognosis
Location, type and identified spread affect the prognosis. In some cats, a local tumour can be removed and good quality of life continues for a long time. Lung metastases and a tumour that is difficult to remove worsen the outlook. A benign lesion may have an excellent prognosis after complete removal.
Survival times in studies describe groups rather than a promised time for an individual cat. Canine survival figures should not be applied to a cat solely on an osteosarcoma diagnosis. Treatment success also considers pain, appetite and voluntary movement.
Prevention
There is no specific prevention, but risk may be reduced through:
- Preventing bone injuries and chronic inflammation.
- Regular veterinary check-ups, particularly for older cats.
- Early investigation of lameness or limb deformities.
Preventing injury benefits general health, but has not been shown to reliably prevent primary bone cancer in cats. Regular examination and investigating new lameness mainly aim for early recognition. A tumour developing does not usually mean you could have prevented it.
Important for cat owners
Bone tumours in cats are serious and often malignant. Remember that limping, avoiding weight-bearing or noticeable bone changes warrant prompt veterinary attention. Early diagnosis improves survival prospects and reduces pain.
This material provides information and does not replace treatment advice. Contact a vet as soon as the first symptoms appear.
Frequently asked questions
Is every bone lesion cancer?
No. An imaging change may relate to inflammation or another bone disease, and benign tumour forms also exist. X-ray findings guide investigation, but a precise diagnosis may require a cell or tissue sample.
Does feline osteosarcoma always spread to the lungs?
Not always. Metastases are possible, and staging is performed before deciding on treatment. The tumour behaves differently in cats and dogs, but newer studies show that spread risk should not be considered insignificant.
Can a cat manage on three legs?
Many cats adapt well after amputation, and removing a painful tumour may substantially improve comfort. The vet assesses suitability individually. Recovery and pain relief are planned according to other health conditions and mobility.
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
- Bone Tumours in Dogs and Cats, Merck Veterinary Manual, accessed 2026-11-02.
- Bone Tumours in Cats and Dogs, American College of Veterinary Surgeons, accessed 2026-11-02.
- Feline osteosarcoma, Texas A&M Veterinary Medical Diagnostic Laboratory, accessed 2026-11-02.
- Osteosarcoma in Cats, VCA Animal Hospitals, accessed 2026-11-02.
- Musculoskeletal neoplasia: An important differential for lumps or lameness in the cat, Journal of Feline Medicine and Surgery, accessed 2026-11-02.
- Diagnosis and clinical outcome of cats with primary appendicular bone tumours: 76 cases, Journal of the American Veterinary Medical Association, accessed 2026-11-02.