When to see a vet urgently
Contact a vet immediately if your cat has any of the following:
- a leg suddenly becomes unusable or changes position;
- severe pain, crying or rapid deterioration after even slight movement;
- breathing difficulty, open-mouth breathing or collapse;
- paralysis, marked unsteadiness or inability to get up;
- inability to eat because of a jaw change.
Overview
Osteosarcoma develops from osteoblasts, the cells that form bone. It can damage limb bones, the spine, ribs and jaws. In around two-thirds of feline cases, the tumour affects a limb bone, most often a hindlimb; the skull, jaws, spine and ribs are affected less often. Do not confuse osteosarcoma with injection-site sarcoma, a soft tissue rather than bone tumour.
The proportions of limb and other skeletal tumours vary between studies; in some, they have been approximately equal. The two-thirds figure therefore does not reliably describe every feline patient population. Tumour location is established individually.
Osteosarcoma arising from bone must be distinguished from soft tissue sarcomas, but the terms are not entirely mutually exclusive: rare bone-forming osteosarcoma also occurs outside the skeleton. Injection-site sarcomas are a separate tumour group that can include different tissue types and, rarely, osteosarcoma. A tissue sample determines the type.
The tumour grows rapidly, causing severe pain, lameness and fractures in weakened bone. Although its tendency to spread is relatively low, local aggressiveness makes osteosarcoma a serious, dangerous disease.
Growth rate and behaviour vary. A lower average tendency to spread than in dogs does not make metastatic risk insignificant in cats. More recent studies of feline limb osteosarcoma have found metastases more often than older estimates suggested. Staging is therefore part of treatment planning.
Causes
The exact causes are unknown, but predisposing factors are considered to include:
- chronic bone injuries and inflammation;
- previous fractures and implants;
- an inherited predisposition;
- older age, over 10 years.
A single cause cannot be identified for most bone tumours. Tumours arising at fracture or implant sites have been described, but an ordinary previous fracture does not mean a cat will develop cancer. The inherited predisposition listed also does not mean a feline risk group equivalent to large dog breeds has been established.
Risk factors
- large and older cats;
- chronic bone and joint diseases;
- previous fractures and operations;
- other tumours.
Evidence on feline risk factors is limited. No consistent breed or sex predisposition has been established. Large size or other tumours alone cannot identify a cat at risk of osteosarcoma. Older cats are affected more often, but ten years is not a diagnostic cut-off: young cats can also develop it.
Typical symptoms
- lameness and reluctance to bear weight;
- pain during movement and examination by touch;
- swelling and altered shape around a bone;
- reduced activity and listlessness;
- fractures without significant trauma;
- with a jaw tumour, difficulty eating, drooling and altered facial shape.
Lameness may start gradually, initially appearing only as avoiding jumps or play. A cat may still eat and otherwise seem fairly normal. Sudden severe lameness may occur when tumour-weakened bone breaks under normal loading. This is called a pathological fracture.
A spinal or skull tumour may cause neurological changes, such as unsteadiness or seizures. Their location guides investigations. However, bone swelling and pain do not establish osteosarcoma alone: other tumours and bone infections can produce similar findings.
Complications and consequences
- bone destruction and fractures;
- severe pain;
- reduced quality of life;
- spread to the lungs and other organs, less often than in dogs but still possible;
- death without treatment.
Treatment goals include controlling local pain and fracture risk while accounting for possible spread. Successful local removal alone does not establish whether the disease has spread. Equally, suspected metastases do not justify delaying pain relief until final results arrive.
Diagnosis at the vet
- X-rays to identify typical bone destruction and new bone formation;
- CT to assess size and plan surgery;
- a bone biopsy for final confirmation;
- a complete blood count and blood biochemistry;
- chest X-rays or CT to look for spread.
As well as the painful area, the vet examines general condition, other limbs and possible neurological signs. If amputation is considered, the ability of the remaining legs to bear weight is assessed. Concurrent joint or other disease affects treatment selection and rehabilitation.
An X-ray may show a destructive bone lesion but cannot always distinguish osteosarcoma from another tumour or infection. A fine-needle sample may help initially; if it is inconclusive, a tissue sample and microscopic examination are needed. The sampling site is planned so it can be accounted for in later surgery. The fracture risk in already weakened bone is considered.
Staging assesses the lungs and other sites where needed, such as abnormal lymph nodes. Node size alone does not establish whether tumour cells are present. CT also helps assess local extent and whether removal is possible. Blood tests provide information about general health and diseases affecting treatment, but cannot confirm osteosarcoma alone.
The pathology report and imaging results are considered together. Microscopic tumour structure and disease extent are different matters. It helps to understand what a sample has confirmed and what still needs investigating for treatment planning.
Treatment
- Surgery is the main treatment, involving amputation of an affected limb or removal of part of the jaw or ribs.
- Radiotherapy can relieve pain and limit growth.
- Chemotherapy is less effective in cats than dogs and is used less often.
- Palliative care provides pain relief and supports quality of life when curative treatment is not possible.
Less frequent chemotherapy use does not, in itself, show poorer effectiveness in cats. There is less research than in dogs. In one more recent retrospective study, postoperative chemotherapy was associated with longer survival in cats without known lung spread before surgery. An earlier study left the role of additional treatment uncertain. These findings do not mean the same treatment suits every patient; discuss potential benefit with a vet experienced in cancer.
The prognosis is somewhat better in cats than dogs because metastases occur less often. Cats may live 1–2 years or longer after surgical removal.
That survival time is not an individual cat's prognosis. A completely removable limb tumour differs from a skull or spinal tumour that is difficult to remove. Metastases, local removability, other health conditions and response affect the outlook. Study populations and follow-up periods also differ.
Home care and recovery
Many cats adapt well to amputation when the remaining limbs function adequately and pain is controlled. Surgery aims to remove the painful tumour site. Both recovery prospects and daily needs are assessed before deciding; the word amputation alone does not determine quality of life.
Follow the surgeon's activity instructions. Prevent uncontrolled jumps and free outdoor access early in recovery, keep the wound dry and prevent licking. Do not apply creams or cleansers yourself. Increasing swelling, discharge, wound opening or bleeding warrants contact.
Keep food, water, a resting place and the litter tray within easy reach. Monitor eating, movement, grooming and interaction, and whether the agreed treatment relieves pain. Record changes for follow-up. Changes to medication or activity are agreed with the practice.
Symptom-relieving care
If the tumour cannot be removed or surgery is not chosen, an active pain management and monitoring plan is still made. Quality-of-life assessment considers appetite, rest, mobility and litter tray use alongside pain. Treatment may combine medicines, environmental changes and radiotherapy where suitable.
Palliative care means relieving symptoms and suffering. Its effectiveness is repeatedly reviewed; persistent pain is not accepted as an inevitable symptom to endure at home. If comfort can no longer be maintained, discuss treatment goals and end-of-life decisions with the vet too.
Prevention
- there is no specific preventive measure;
- take older cats for regular veterinary checks;
- monitor health after chronic bone injuries and fractures.
Important for cat owners
Osteosarcoma is a serious cancer in which early diagnosis is crucial. Remember that lameness, swelling and painful bony lumps are warning signs requiring prompt veterinary attention. The earlier treatment begins, the better the chance of preserving life and good quality of life.
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
Can osteosarcoma in cats spread to other organs?
Yes. A lower average tendency to spread than in dogs does not remove the risk. Chest investigations and assessment of other findings help plan treatment and estimate prognosis.
Is every painful bone lump osteosarcoma?
No. Other tumours and infections can occur in the same area. Imaging shows the damage, but tissue examination is often needed to establish the precise type.
Does a cat always need chemotherapy after amputation?
Not automatically. Additional treatment is considered according to tumour type, spread, research evidence and other health conditions. Benefits and adverse effects are discussed individually.
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 2026-11-03.
- Bone Tumours in Cats and Dogs, American College of Veterinary Surgeons, accessed 2026-11-03.
- A retrospective Italian Society of Veterinary Oncology (SIONCOV) study of 56 cats with appendicular osteosarcoma, Veterinary and Comparative Oncology, PubMed, accessed 2026-11-03.
- Diagnosis and clinical outcome of cats with primary appendicular bone tumours: 76 cases, Journal of the American Veterinary Medical Association, PubMed, accessed 2026-11-03.
- Musculoskeletal neoplasia: An important differential for lumps or lameness in the cat, Journal of Feline Medicine and Surgery, accessed 2026-11-03.
- Section 3: Tumour Diagnostics and Staging, AAHA, accessed 2026-11-03.
- 2023 AAFP/IAAHPC Feline Hospice and Palliative Care Guidelines, American Association of Feline Practitioners and IAAHPC, accessed 2026-11-03.
- Guideline for Feline Injection-Site Sarcoma, European Advisory Board on Cat Diseases, accessed 2026-11-03.
- Osteosarcoma in Cats, VCA Animal Hospitals, accessed 2026-11-03.
- Care of Surgical Incisions in Cats, VCA Animal Hospitals, accessed 2026-11-03.