Bone Tumors in Cats

The most common type of bone tumor is osteosarcoma. This is a serious condition, but it is significantly less aggressive in cats than in dogs. These tumors are often located in the radius, tibia, femur, or humerus, and are more commonly found in the hind legs than the front. The condition can affect cats of any age, but is most common in those ten years of age or older.

If cat is limping without explanation, a trip to the vet is in order. Although there are many possible causes, a bone tumor is a significant enough concern to warrant attention. Finding and treating a tumor as early as possible is a key factor in achieving a positive outcome. 

Bone tumors are growths commonly found on the leg bones of cats. Less often, tumors can develop on the spine, ribs, pelvis, shoulder blades, and skull. Cats are much less likely to be affected by this condition than dogs, and approximately one-third of bone tumors found on cats are benign.

Symptoms can vary depending on the area in which the tumor is located. Owners should keep an eye out for one or more of the following:

• Lameness
• Swelling of affected area
• Stiffness
• Limited joint movement
• Visible lump or mass
• Pain in the affected area
• Muscle atrophy
• Bone fractures not caused by injury
• Difficulty eating (jaw tumor)
• Seizures or wobbling (skull or vertebral tumors)
• Difficulty breathing (rib tumors)
• Discharge from nostrils (nasal bone tumors)
• Difficulty with defecation (pelvic bones tumors)

Bone tumors are classified as either primary or secondary. Primary tumors develop directly on the bone. Osteosarcoma is the most common primary tumor and accounts for 95 percent of bone tumors. Other types include chondrosarcoma, fibrosarcoma, and hemangiosarcoma. Secondary tumors, rarely seen in cats, are often spread from a nearby site, as is the case in multiple myeloma of the bone marrow. Secondary tumors may also have metastasized from tumors in another area of the body. 

Osteosarcoma and other primary tumors usually happen spontaneously. Studies have been unable to pinpoint a cause, and no genetic link has been found. There is no conclusive evidence of the condition occurring one gender over another. There is some evidence that large and giant-breed cats may be more likely to develop the condition. In rare cases, tumors may arise in areas where the bone was previously damaged by fractures, radiation treatment, or bone diseases.

The first step in diagnosing bone tumors in cats is a complete physical exam and x-rays of the affected area. An orthopedic exam will be completed to rule out other conditions that may be causing the symptoms. If a veterinarian suspects a bone tumor, he or she may consult with a veterinary oncologist and/or surgical specialist. 

Additional tests will be needed to determine the type of tumor present, whether it has spread to or from other areas of the body, and the overall physical condition of the cat. It is likely that the veterinarian will recommend a blood analysis to determine blood count and serum biochemistry and a urinalysis to assess kidney function. A full body scan done with a radioactive marker that is injected into the bloodstream can highlight any additional bone tumors that may be present. A chest x-ray is sometimes recommended to check for tumors in the lungs that may have spread to the bone. A biopsy or needle aspiration should also be done in order to determine the specific type of tumor that is present. This is critical to developing an effective treatment plan as different types of tumors react differently to various treatments.

Treatment plans will vary depending on the size, location, and type of tumor. Other considerations include whether it is localized or has spread and the general health of the affected animal.

Curative-Intent Treatment

The purpose of curative-intent treatment is to improve the animal’s quality of life, minimize the risk of metastasis, and ultimately cure the tumor. For cats with any type of primary bone tumor, the only option is surgery. Limb amputation is most commonly recommended for primary bone tumors. A thorough examination of the cat will need to be completed to determine whether it will be able to function on three legs. If the cat is unusually heavy or has arthritis or hip dysplasia, this may not be a viable option. The veterinarian will determine whether post-surgical chemotherapy is needed to reduce the risk of metastasis. Cats with osteosarcoma may be treated with the assumption that there are also tumors located in the lungs.

Limb-sparing surgery occurs when the affected part of the bone is removed and replaced with a tissue graft from one of the other legs. This is not as commonly available and comes with a high risk of complications. Your veterinarian will help to determine whether this is an option for you.

Palliative Treatment

When an animal is not a candidate for curative-intent treatment, the focus turns to controlling pain and helping to keep it as comfortable as possible. Medication is the most common treatment, as it can reduce pain and help to prolong life even when the tumor cannot be removed. Radiation once a week for three to four weeks may be used to treat pain and inflammation. In extreme cases where the tumor is causing a significant amount of pain, limb amputation may also be recommended.

For cats that have been diagnosed with bone tumors, the outlook can be described as “guarded.” If the condition is not treated, cats are likely to live less than a few months. With treatment, cats with bone cancer can live an average of two years or longer. The prognosis is good when the tumor has been completely removed and the cancer hasn’t spread. When osteosarcoma is present, amputation of the affected leg without follow-up chemotherapy results in a mean survival time of 350 days to four years.

Following surgery and chemotherapy, it is likely that cats will experience a loss of appetite. Providing a highly nutritional diet and a comfortable place to eat and sleep will assist in recovery. Animals tend to adapt to limb amputation within three to four weeks. Owners should remain patient and offer assistance when possible. It may be helpful to provide ramps or stairs to minimize the need for jumping. Carefully monitor your cat during recovery time, and don’t hesitate to speak to your veterinarian about additional pain medication if you feel that it may be needed.