What is Osteosarcoma?
Osteosarcoma is the most common primary bone tumour in dogs. It is a malignant bone tumour that predominantly affects the bones in the limbs (appendicular osteosarcoma), but can also much less commonly affect bones of the skull, spine and ribs (termed axial osteosarcoma).
The most common sites are the distal (bottom) part of the radius and the proximal aspect (top) of the humerus, the distal aspect of the femur and the proximal aspect of the tibial bones, however it can occur in other parts of the bones.
There is no known definitive cause for osteosarcoma, however it is thought to be related to genetics due to the predisposition of the disease to large and giant breed dogs.
What breeds are most commonly affected?
Osteosarcoma can affect any breed of dog and can occur at any age, but it will typically present in older, large and giant breed dogs such as the Great Dane, Bull Mastiff, Irish Wolfhound and Rottweilers.
What are the clinical signs of Osteosarcoma?
The most common signs that will be seen are a hard swelling over the bone in one of your pets limbs. They will commonly also develop lameness on the same limb. This lameness will be persistent and will not resolve with rest or painkillers, which is often the first treatment for lameness in a dog. The firm swelling is often extremely painful to the touch, and your pet will resent you touching the limb.
As the disease progresses, the bone will become weakened by the tumour and will eventually fracture, termed a pathological fracture. This is sometimes the first sign that a problem is present, as dogs are quite stoic and may not show clinical signs of lameness until a fracture occurs.
How is Osteosarcoma diagnosed?
During the diagnostic process we are aiming to not only investigate the location and extent of the primary tumour, but we must also determine the presence and also the extent of any spread (metastasis) throughout the body at the time of presentation. This is termed ‘staging’.
Initially a complete physical examination and basic blood and urine testing will be performed to assess the general health of your pet. This will detect any other underlying disease and help us assess your pet for their ability to undergo treatment.
Radiographs of the affected limb (or skull/ribs if applicable) will be performed to assess the limb and rule out any other conditions (such as a traumatic fracture, infection etc), and to assess the extent of the cancer in the bone. Radiographs also allow us to see if the cancer has crossed into neighbouring bones or joints. Radiographs of the chest and lungs will also be performed at the same time. This is because osteosarcoma is a highly malignant cancer, with the most common site of spread being the chest and lungs. If the cancer is visible in the chest and/or lungs at the time of presentation, this unfortunately will greatly decrease the prognosis.
CT scanning is a more advanced imaging technique compared to radiographs, and will enable us to detect much more subtle changes in the chest and lungs. Radiographs can only pick up neoplasia in the lungs once it has grown to a certain size, and as such there is the risk that the cancer has spread to the lungs but has not grown to a size large enough to be visible on radiographs. This is where CT is helpful in assisting our diagnosis and determining the prognosis. CT scanning will also enable us to reconstruct the bone and the tumour in 3D and will enable us to determine if the limb can be saved.
Whilst the radiographic appearance of Osteosarcoma is normally relatively specific, it can be confused for a number of other, less aggressive neoplasia or infectious (bacterial, fungal) processes. In most cases we will recommend a bone biopsy prior to any other surgical intervention. This requires a special biopsy needle to be inserted into the bone whilst your pet is under general anaesthesia, which will obtain a small sample of bone. This is sent to the laboratory for analysis and for confirmation of the diagnosis.
What are the treatment options for Osteosarcoma?
Unfortunately there is no ‘best’ way to treat all bone cancers in dogs. The best treatment option for you and your pet will depend on a number of factors and is a very personal decision for you and your family. The most important thing for you and your family to understand is that, unfortunately, by the time that your pet is showing clinical signs of osteosarcoma, and by the time that we diagnose osteosarcoma, cells of the cancer have almost certainly spread from the primary bone tumour to elsewhere in the body (metastasis will almost always have occurred at the time of diagnosis). Often these cancer cells are unable to be detected, even with CT scanning, and will often remain dormant (not causing any problems to your pet) for months or even years. This must always be kept in mind when you are deciding on which treatment option will be best for your family and your pet.
The primary goal of treatment is to relieve bone pain and re-establish a good quality of life for your pet. Treatment revolves around not only treating/removing the primary bone tumour that your pet will have presented to us for, but also preventing the progression of growth of metastatic cells into secondary tumours that will cause other problems for your pet (most commonly weight loss and weakness, with some patients experiencing breathing problems such as coughing).
Pain Relief: Whilst decisions are being made on the best treatment option for your pet and your family, we will prescribe a number of different pain-relief medications for your pet. Osteosarcoma is an extremely painful disease and the main goal in treatment is to make your pet more comfortable. A number of different type of pain relief drugs will be dispensed, including pain relief, anti-inflammatory medications, and neuropathic pain relieving medications.
Amputation: Amputation is the most common treatment option that we perform here at NCVS, either without or in conjunction with chemotherapy. Amputation has advantages in that it removes the primary bone tumour, and therefore the source of significant pain to your pet. Amputation is the most reliable way to end bone pain, minimise the complications associated with bone tumours, and to prevent the development of a pathological fracture (if there is not one already present). We find that most patients respond extremely well to amputation and are often up and walking the day after surgery. Amputation is a big decision, and other factors must be considered when deciding on amputation. For example, if your pet suffers from other orthopaedic or neurological conditions, then they may not be able to cope with the loss of a limb, and other treatment options must be decided upon.
Following amputation, your pet’s limb will be submitted to a laboratory for histopathology to confirm the diagnosis, ensure we have obtained all the tumour, and to grade the tumour (determine how aggressive it is).
Chemotherapy: Chemotherapy addresses the second goal of treatment – preventing the progression of growth of metastatic cells into secondary tumours – and promotes longevity of your pet. Chemotherapy is most often performed in conjunction with amputation to provide the best results. Our medicine service will discuss the exact protocol with you during consultation, and make sure you are aware of the side-effects and prognosis for your pet.
Luckily, dogs do not often experience the same side-effects following chemotherapy that people do, but we will occasionally see inappetance, nausea, lethargy and diarrhoea for a short period after a treatment (often only a day or so). In humans, the aim of chemotherapy is complete remission where in dogs we aim extend their life as much as possible while keeping good quality of life for them.
Radiation Therapy: Radiation therapy can be used to treat bone pain that is related to cancer. Unfortunately, we do not have the abilities to do this in-house, but we will refer your pet to clinics in Brisbane for this treatment if you decide on this option. The important thing to recognise about radiation therapy is that it only targets the primary bone tumour and does not assess any metastases in the body.
What is the prognosis?
Unfortunately, despite our best efforts and use of multiple different treatment modalities, dogs with appendicular osteosarcoma will almost certainly die from the disease. This may be from the primary bone tumour causing uncontrollable pain (this most commonly occurs when the limb cannot be removed due to other orthopaedic/neurological problems), or to the development of secondary tumours (metastasis) that cause secondary clinical signs. As described above, we most commonly experience metastasis to the chest or lungs, which can present with weight loss, weakness, coughing or other breathing problems.
The prognosis will be influenced by several factors. This includes the degree of spread (metastasis) at the time of diagnosis, the aggressiveness of the tumour, the general health of your pet, whether chemotherapy is elected, and which bone is affected.
The following figures are average values for survival, depending on different treatment options. When reading these figures you must remember that 50% of patients will do better than these numbers, but unfortunately 50% of patients will also do worse.
– Palliative care alone (pain-relief medication): 1-3 months
-Amputation alone: 4-5 months
-Amputation and chemotherapy: 10-12 months
-Limb sparing and chemotherapy: 10-12 months
-Radiation and chemotherapy: 8-10 months