Osteosarcoma

What is an osteosarcoma?

An osteosarcoma is a tumor that consists of degenerated bone cells. These cells multiply uncontrollably and form a soft, non-calcified bone substance known as an osteoid. The osteoid destroys and displaces the healthy bone, making it unstable and brittle. It also irritates the periosteum, which is very sensitive to pain.

Osteosarcoma occurs most frequently in the limbs, especially on the front legs near the elbow and on the hind legs near the knee joint. However, it can also occur in other areas of the skeleton, such as the skull, spine or pelvis.

Osteosarcoma is the most common bone tumor in dogs and accounts for around 85% of all bone tumors. It mainly affects middle-aged and old dogs, but young dogs can also develop the disease. There is a genetic predisposition for some breeds, such as the Bernese Mountain Dog, Great Dane, Rottweiler, Doberman, Irish Setter or German Shepherd.

What are the symptoms of osteosarcoma?

The first and most obvious symptom of osteosarcoma is sudden lameness in a leg or limb. The lameness is usually permanent and cannot be alleviated with painkillers. The dog also shows pain when touching or moving the affected area.

In addition to the lameness, there may be swelling of the tissue around the bone, which is sometimes visible or palpable. The swelling may be warm or hard and may become inflamed or ulcerated. In advanced cases, a spontaneous bone fracture may occur, which is referred to as a pathological fracture.

Another symptom of osteosarcoma is weight loss or loss of appetite in the dog. This is because the tumor consumes a lot of energy and weakens the immune system. The dog may also appear lethargic, tired or depressed.

How is osteosarcoma diagnosed?

If you notice lameness or swelling in your dog, you should see a vet as soon as possible. The vet will perform a thorough physical examination and look for other signs of osteosarcoma.

To make a diagnosis, the vet will usually perform an X-ray examination of the affected bone. Typical changes in the bone can be seen on the x-ray, such as a breakdown or build-up of bone substance. Sometimes the tumor itself can also be seen.

To make sure that it is an osteosarcoma and not another disease such as an infection or arthritis, the vet can also take a tissue sample (biopsy). This involves taking a small sample of the tumor under local anaesthetic or general anaesthetic and examining it under a microscope.

To determine whether the tumor has spread to other organs, the vet may also carry out further examinations such as a blood test, an ultrasound scan or a computer tomography (CT) scan. These tests can also help to determine the best treatment option for the dog.

How is osteosarcoma treated?

Treatment for osteosarcoma depends on several factors, such as the dog's age and health, the stage and location of the tumor, and the owner's wishes. The treatment has two goals: to relieve the pain and to prolong the dog's life.

The most common and effective treatment for osteosarcoma is amputation of the affected limb. Amputation completely eliminates the tumor and pain and prevents a pathological fracture. Most dogs manage very well with three legs and have a good quality of life.

However, amputation alone is not enough to cure the dog, as in most cases the tumor has already spread. Chemotherapy is therefore usually recommended to slow down or prevent the formation of metastases. Chemotherapy consists of several sessions during which the dog is given drugs that kill the cancer cells or inhibit their growth. Chemotherapy can have side effects such as nausea, vomiting or hair loss, but these are usually mild and temporary.

An alternative or complementary treatment to amputation is radiotherapy. This involves irradiating the tumor with high-energy rays that destroy or damage the cancer cells. Radiotherapy can relieve pain and slow down the growth of the tumor, but not stop it. Radiotherapy can also have side effects such as skin irritation or hair loss.

Another treatment option is pain therapy. The dog is given painkillers such as non-steroidal anti-inflammatory drugs (NSAIDs) or opioids to reduce the pain or make it more bearable. Pain therapy can be used alone or in combination with other treatments. However, pain therapy does not cure the dog and can also have side effects such as gastrointestinal problems or kidney damage.

What is the prognosis for osteosarcoma?

Unfortunately, the prognosis for osteosarcoma is poor. Without treatment, the average survival time is only around two months after diagnosis. With amputation and chemotherapy, the survival time can be extended to around one year. Only about 10% of dogs survive longer than two years after diagnosis.

The prognosis depends on various factors, such as the age and health of the dog, the stage and location of the tumor, the type and success of the treatment and the dog's individual response to the therapy.