OSTEOSARCOMA

Bone tumours usually affect various parts of the spine, namely the axial (ribs, spine, scapula, pelvis and skull) or the appendicular (limbs). There are two classifications of these tumours. They are either primary which means that they form directly in the bone or are secondary which refers to a tumour spreading from a site adjacent to the bone. For example, it may come from multiple myeloma of bone marrow or even transitional cell carcinoma from the urinary tract. The four most prominent bone tumours are: chondrosarcoma, hemangiosarcoma, osteosarcoma and fibrosarcoma. The most common of the bone tumours which also accounts for the majority of bone tumours identified is osteosarcoma. Appendicular osteosarcoma in dogs, is extremely aggressive. The treatment is fairly intensive and includes the surgical resection followed by chemotherapy so that the tumour cells are less likely to spread (metastasize) to the lungs or other bones.

It is common for primary bone tumours, especially osteosarcoma, to have a spontaneous appearance without a known or possible cause. The genetic predisposition of Scottish Deerhounds makes them more likely to develop osteosarcoma. This tumour is also quite common in larger breeds of dogs, such as Rottweiler. The risk of osteosarcoma is much higher in Giant or large breed dogsas well as older dogs. However, smaller and younger dogs can also develop osteosarcomas.

Primary bone tumours are rare in cats. In dogs, the majority of the tumours are malignant whereas almost a third of tumours in felines tend to be benign. Osteosarcoma is also the most often identified bone tumour in felines, however it is not as aggressive as those found in dogs.

Sites where previous damage to the bone occurred can potentially develop a tumour. Types of bone damage which is associated with primary bone tumours are:

• fractures
• bone diseases
• bone cysts
• benign bone tumours
• infarcts (which are areas where the bone does not receive blood supply)
• radiation therapy
• orthopedic implants such as products used to repair fractures and for total hip replacements

However, it is important to know that it is rare for tumours to develop in the before mentioned cases and usually develop without an apparent cause.

Tumours on the appendicular skeleton often present signs of swelling or lameness in the area of the bone affected by the disease. There is a variable degree and onset of lameness. It is more common for the lameness to develop slowly and become more serious weight-bearing lameness later on. However, acute and non-weight-bearing lameness is possible if a fracture occurs in the area the bone tumour has weakened. This is known as a pathologic fracture. If metastasis (spreading of cancer) to the lungs occurs, all limbs may become swollen (hypertrophic osteopathy) along with general weakness and difficulty with respiration (breathing). Systemic illness seldom occurs where the primary bone tumours have not yet spread to other areas.

Symptoms of axial skeleton primary bone tumours are dependent on the specific bone involved. The most common first signs of a tumour are swelling or a mass, usually in the ribs, skull or jaw. Other potential signs are:

• Struggling to eat (jaw tumours)
• Neurologic signs such as wobbly gait or seizures (skull or vertebral tumours)
• Difficulties with respiration or lameness (rib tumours)

Signs and symptoms of secondary bone tumours are dependent on which bone or bones are affected. It can be very difficult to differentiate between a primary and secondary bone tumour if there are no clinical signs associated with the primary tumour, for example difficulty urinating if the tumour is located in the prostrate or urinary bladder.

“Staging” is the process of evaluating the diagnostics of a possible tumour. Your veterinarian, potentially with the aid of a specialist such as an oncologist, can perform a range of tests to determine which tumour type your dog is suffering from, where the tumour has potentially spread to and the overall wellbeing of your pet. These are:

• Orthopedic or physical examinations
• Blood tests which are made up of serum biochemistry and complete blood count
• CT scans or chest radiographs
• Radiographs of the bone
• Bone scans of the whole body
• Fine needle aspiration and biopsy

Physical examination would be needed to determine the general health of a pet as well as to identify any other issues. Orthopedic examination is essential in order to determine which bone is affected, and to rule-out reasons for lameness such as neurological disease or hip dysplasia for example and also to decide if the pet will be able to function if limb amputation is required. It is also important that general health is checked through blood tests, thus other health issues can be taken into account when creating a suitable treatment plan for the patient as many are older pets with underlying problems. Kidney function may be assessed through a urinalysis. In the case where the veterinarian is considering a limb-saving procedure, bone scans, radiographs and advanced imaging are essential in order to determine extent of the tumour involvement and the best procedure to follow through with.

In order to determine the best way forward, a biopsy will be necessary. This is because tumours react differently to various types of treatments. A sample of the suspected tumour will give your veterinarian an idea of the most suitable treatment. Biopsy is usually recommended when the case is rarer, such as a middle-aged dog, smaller breed dog, multiple lesions or lesions that are present in the middle of the long bones instead of at the end. It is also recommended when there is suspicion of other diseases such as a fungal bone infection.

If there is extensive destruction of the bone, a biopsy prior to surgery may not be necessary as it will not have an effect on the treatment plan. In this case, pathologic evaluation is the better option after the limb-sparing procedure or amputation has been conducted. Sometimes the patient will be screened for cancer through fine needle aspiration, however, it is more often that a bone biopsy is needed (where an actual sample of the tumour is extracted for reviewing by a pathologist).

Appendicular osteosarcoma is extremely metastatic and malignant in canines. The lungs are a common site for metastasis. Often CT scans or chest radiographs need to be performed to evaluate metastasis into the lungs. Bone metastasis occurs about as often as lung metastasis; however, it is more difficult to manage as the risk of the bone fracturing is increased when there is an increase of weight bearing following limb amputation. The best way to evaluate the presence of a metastatic disease in any bone is through a whole-body bone scan. However, it may be difficult to access nuclear medicine facilities. Alternatively, you could use a whole-body radiograph. This method is time consuming and expensive; it is also not quite as sensitive as a bone scan and can miss metastasis and other changes in the bone.

Axial skeleton tumours are best assessed by a CT scan which will allow your veterinarian to determine whether surgery will be possible and which one will produce the best outcome. After surgery, the tumour will be sent to a pathology lab in order to assess the type and grade of tumour as well as to tell if surgical margins no longer have tumour cells or if it has spread to regional lymph nodes.

Appendicular skeleton primary bone tumours can be treated through curative-intent or palliative methods. The aim of palliative treatment for the pet is to reduce pain and better the pet’s quality of life. It does not however necessarily prolong life. Curative-intent treatment, however, is aimed at bettering quality of life as well as controlling the spread and attempting to cure the tumour. There is a very slim chance that this will be achieved with this type of tumour.

Palliative treatment includes radiation therapy, surgery and drugs to minimize pain. Many drugs are analgesic (pain-killing), however, the degree of pain relief of different drugs varies. Initially, non-steroidal anti-inflammatory drugs usually prove sufficient. With progression of the tumour, stronger analgesic medication may be needed. Radiation therapy can be efficient in reducing inflammation and pain. It is often used alongside pain medication and chemotherapy. There are various protocols determining the irradiation process of the bone tumour, the most common one being once a week for a 3-to-4-week period of time. Amputation is also an option if there are extreme levels of pain or if the bone is fractured. Amputating the limb without chemotherapy is used as a palliative option as well as it does not result in a longer life expectancy.

Curative-intent treatment is an option for appendicular osteosarcoma in dogs for attempting to treat the tumour and minimize the risk of metastasis. To treat the local tumours, it is often necessary to amputate the limb. If the tumour is located in the pelvis or hip, removal of a part of the pelvis can be done. A large portion of dogs tend to adapt well post-amputation, including those who are overweight, large breed or arthritic. Recovery and adaptation take approximately 4 weeks and is even better when the owner shows a good attitude towards the recovering dog. The alternative option is limb-sparing surgery which keeps function an anatomy of the impacted region. There are various limb-salvaging methods to choose from, however a lot of them only apply to the distal radius which is the bone found adjacent to the carpus or wrist. Stereotactic radiation is an example of a non-surgical limb-sparing technique which could be used in other locations. Limb-sparing surgery has no advantage over amputation other than preserving limb function. Pet owners usually prefer limb-sparing surgery; however, it is not always available and the likelihood of complication is quite high. After treatment, the tumour should be sent to a veterinary pathologist for testing.

Surgery is usually necessary for dogs with primary bone tumours besides osteosarcoma and hemangiosarcoma and cats with any primary bone tumour. The likelihood of the bone tumour metastasizing in cats post-surgery is low, therefore chemotherapy is not necessary. Appendicular chondrosarcoma in dogs can potentially metastasize, however chemotherapy does not have any positive effect on this nor on survival time. Dogs that have appendicular osteosarcoma should go through chemotherapy as it has proven to have a significant impact on survival time post-surgery. Chemotherapy often begins around 10-14 days after surgery. There are a range of chemotherapy options for dogs with osteosarcoma. It is essential to consult an oncologist for information about costs and side effects of your different options.

The location and size of an axial skeleton primary bone tumour will determine which treatment is suitable. Axial bone tumours are usually treated through surgery such as craniectomy, chest wall resection, mandibulectomy and reconstruction of ribs. Scapular tumours could be removed through a total or subtotal scapulectomy (shoulder blade is affected). In the case of pelvic tumours, a hemipelvectomy can be performed, which requires a section of the pelvis to be removed in addition to amputation. When surgery is unwanted or not possible, palliation can be achieved through analgesic drugs or radiation therapy. The chances of metastasis is low with regards to axial skeleton bone tumours, thus chemotherapy is not always necessary after surgery. However, dogs with osteosarcoma of the scapula, ribs and pelvis should receive chemotherapy due to high metastatic rates. Mandibular osteosarcoma also needs chemotherapy treatment.

Limb amputation may often be the best option and recommended, especially because of the low complication rate. Complications which could arise, however are very rare, are wound breakdown or infection or fluid accumulation under the surgical location. Limb-sparing complication rate is usually much higher. The common complications with this option include, implant failure, infection, or recurrence of the tumour. These complications are much more common that those associated with amputation. The biggest one being infection in limb-sparing patients. Antibiotics can be used to control the infection, but may not cure it. Treating limb-sparing-related infections can also be done through implanting antibiotic-impregnated beads. This may decrease the overall risk of infection.

Chemotherapy is aimed maintaining a good quality of life for the pet while attempting to kill the tumour. A large majority (above 85%) of cats and dogs will go through chemotherapy with few or no problems. Some cases require the pet to be admitted to hospital due to chemotherapy-related problems. These can be dehydration from diarrhea and vomiting, bone marrow suppression and infection. The severity and risks of complications due to chemotherapy are different depending on the particular drug used. This should also be discussed with an oncologist.

After amputation, most dogs will take about 12-24 hours to walk without assistance. Encouraging the dog to exercise is essential for a faster recovery speed. The wound should be inspected at least twice a day for possible signs of breakdown or infection (dehiscence). You should look for redness, swelling, pain and discharge.

In the case of limb-sparing surgery, there should be a bandage wrapped lightly over the limb which needs regular changing for a two to three week period. The pet can begin exercising immediately after surgery; however, it should be only walks on a leash for the first four weeks. Exercise is essential to prevent the toes contracting and minimise how much the toes and feet swell. These can occur due to exercising certain blood vessels or muscles during surgery.

Dogs with appendicular osteosarcoma will survive for on average 90 to 175 days after palliative treatment. However, chemotherapy in conjunction with palliative radiation treatment have an average of 300 days survival after the process. Treatment with curative-intent has a much higher chance of the dog living for a longer period of time with the average being 235-366 days with some pets living a further 2+ years. Blood tests are analyzed prior to surgery in order to look at alkaline phosphatase. This enzyme has proven to have an association with how long a pet will survive after operation and chemotherapy. A normal reading at the time of diagnosis indicates that the dog will potentially live for longer compared to one with an increased level of the enzyme. Prognosis in dogs can also be affected by tumour size, location and its histologic grade.

Dogs diagnosed with appendicular chondrosarcoma can live from 540 to 2618 days, following limb amputation only. It is essential that chondrosarcoma is graded in order to have an accurate depiction of the survival time as it is significantly different for each grade. Metastasis is likely to occur, usually later in the course of the illness, regardless of chemotherapy or lack thereof.

It can be difficult to determine a prognosis for appendicular fibrosarcoma or hemangiosarcoma as these are rare. Regardless, metastasis has proven to be very common in hemangiosarcoma patients and thus the survival period is much lower post-amputation.

Appendicular osteosarcoma in cats is less likely to metastasize, resulting in a high median survival time of 350 days which could extend to 4 years.

An accurate prognosis for axial bone tumours depends on the location and tumour type. Pelvis and scapula osteosarcoma often have a similar prognosis to that of appendicular osteosarcoma cases, for both curative-intent and palliative treatments. Osteosarcoma of the head has poor survival times usually due to the tumour reoccurring in the same area. In the chance that the tumour is completely resected, the dog will be cured and their survival time will increase drastically, thus aggressive surgical treatment is usually necessary in such cases.

The skull bones could also be affected by multilobular osteochondrosarcoma which is an axial skeleton tumour. Prognosis in this case is dependent on histologic grade and whether or not the tumour was completely removed. If the tumour resection was not complete, there is a higher chance of recurrence and metastasis. The overall average survival, with regards to all histologic and resection cases, is approximately 600 to 800 days. Multibular osteochondrosarcoma tumours grow slowly, thus after the dog is diagnosed with metastatic disease, their survival time will still be prolonged for a average of 239 days.

Rib osteosarcomas are regarded as aggressive tumours. Metastasis is diagnosed at death for majority of cases in osteosarcoma, hemangiosarcoma and fibrosarcoma. Prognosis in dogs suffering from rib tumours, can be affected the type of tumour and how complete the surgical resection is. The survival period for dogs diagnosed with rib osteosarcomas is only around 90 after surgical treatment which can be increased to around 290 days when combined with chemotherapy. Rib chondrosarcoma has a longer 5 to 10 times higher survival period post-surgery in comparison.

For dogs with vertebral tumours prognosis is generally poor. If the tumour is malignant, the average survival is around 135 days, this is regardless of the type of tumour. Factors such as location of the tumour and post-operative treatment do not seem to impact the survival chances of these tumours.