The final stages of osteosarcoma in dogs are characterized by spread to secondary tumors mostly localized to the lungs. This translates in dogs showing respiratory signs. In order to better understand what happens when bone cancer in dogs worsens, it helps to firstly understand how this type of cancer impacts the dog's body. Does the limping worsen considerably? Is the dog in great pain? What can be done to keep the dog comfortable at the last stage? Veterinarian Dr. Ivana, discusses the final stages of osteosarcoma in dogs.
Understanding Osteosarcoma in Dogs
Osteosarcoma is an extremely aggressive and malignant type of bone cancer. Accounting for about 5 percent of all canine cancers, osteosarcoma is the most common type of bone cancer. Each year, nearly 10.000 dogs are diagnosed with osteosarcoma.
Although it can affect any bone in the body, in 80 percent of the cases, osteosarcoma occurs in the limbs. Sadly, by the time a diagnosis is made, 90 to 95 percent of the patients will have developed secondary tumors or metastasis. In almost all cases, the secondary tumors are located in the dog's lungs.
As with many other types of cancers, the exact cause for osteosarcoma is unknown. However, genetics, hormones, pesticides and previous bone trauma are confirmed risk factors.
Osteosarcoma is more common among older dogs (7 to 9 years of age), but it can also be diagnosed in young dogs (18 to 24 months of age). The disease is more frequently reported in males than in females.
Large and giant dog breeds are at higher risk of developing osteosarcoma. The most frequently affected breeds include Boxers, Weimaraner, Irish Setters, Saint Bernard, German Shepherds, Labrador Retrievers, Golden Retrievers, Mastiffs, Rottweilers, Dobermans, Great Danes, Greyhounds, Great Pyrenees and Irish Wolfhounds.
Last but not least, according to medical reports, osteosarcoma is more likely to develop on the front leg rather than rear leg. The shoulder and the wrist are most frequently affected.
There are various types of osteosarcoma in dogs. Based on where it is located, there are three main different types of osteosarcoma: 1) Appendicular – if located on the long bones of the extremities, 2) Axial – if located on the skull, spine or dog's ribs and 3) Extraskeletal – if located on a non-bony tissue such as the mammary glands, the spleen, the liver or the kidneys. Appendicular osteosarcoma (bone cancer of the dog's legs) is the most common type of osteosarcoma in dogs.
Diagnosis of bone cancer is dogs is usually set through x-rays. On the image, the lytic bone changes are often described as "moth-eaten" and help confirm the diagnosis. On the x-ray image it is important to differentiate between osteosarcoma and bone infection. To do so, it is advisable to check the joints. Osteosarcoma does not cross joints, while bone infection does. Biopsy, CT, MRI, abdominal ultrasound and spinal fluid analysis are performed to stage the cancer and prepare a better treatment strategy.
The Final Stages of Osteosarcoma in Dogs
The tumor starts forming deep inside the bone, and as it grows, it moves outward. Simply explained, when the tumor develops it's as if the bone is slowly exploding from the inside. As the condition progresses, lameness tends to go from intermittent to constant over the course of 1 to 3 months.
As the osteosarcoma develops, it consumes the normal bone structure, and as a result, the strong and healthy bone tissue is replaced with porous and weak cancerous bone-like tissue. The weakened bone-like tissue is extremely prone to fractures. These fractures, occurring due to pathological changes in the bone structure, are scientifically known as "pathological fractures."
The problem with pathological fractures is that they lack the ability to heal. Therefore, there is no point in surgically stabilizing them or placing casts. Obvious swelling of the affected bone will appear as normal bone is replaced by tumorous bone.
The sudden bone fractures, lameness and swelling are the basic clinical signs indicative of osteosarcoma. It goes without saying that osteosarcoma is an extremely painful condition.
To make matters worse, the cancer spreads to other body parts, and as mentioned, the lungs are the most commonly affected and by the time the tumor is found in the leg, it is considered to have already spread. When the secondary tumors grow in size, therefore coughing and difficulty breathing are likely to develop due to secondary lung cancer.
Making Dogs With Bone Cancer Comfortable
Generally speaking, the treatment for osteosarcoma includes 3 steps: pain management, surgery and chemo. Let's take a closer look at these treatments.
As stated, osteosarcoma is extremely painful and requires a carefully combined mix of different pain killers such as NSAIDs (carprofen, firocoxib, deracoxib, etodolac, meloxicam), opioids (morphine, methadone) and neuropathic pain meds (gabapentin, amantidine).
Palliative radiation alleviates the pain associated with the primary tumor. However, it does not affect secondary, distant tumors. Lately, the use of bisphosphonates (bone-hardening drugs used in menopausal women) have been recommended. These drugs not only strengthen the bones, but also alleviate cancer-induced pain.
Surgery can be either amputation or limb-conserving surgery. Some vets prefer amputation since it completely eliminates the source of pain, helping dogs with bone cancer be more comfortable. Others recommend limb-sparing surgery for dogs with bone cancer because of its effect on the quality of life. In this surgery, the tumor is removed and the gap of bone is bridged with bone grafts or implants. Surgery does not increase the survival time, but it favors a less painful or painful free rest of life.
Chemotherapy is meant to delay the progression of the secondary tumors. The benefits of chemotherapy should be individually assessed. It should be noted that dogs are less prone to developing chemotherapy provoked side-effects than humans. However, some dogs may experience transient lack of appetite, nausea, loose stools and lethargy.
Palliative Care For Dogs With Bone Cancer
Regardless of the treatment strategy, home care is crucial. Here are several tips for making your dog more comfortable during the final stages of dog osteosarcoma:
- Place elevated and easily accessible food and water bowls in several different locations around the house
- Provide a therapeutic, heavily-padded foam bed
- Make sure all surfaces are non-skid and padded
- Use indoor pee pads or diapers
- Use mobility aids such as car ramps and dog stairs
- Keep your furniture arrangements stable
- Limit all forms of stress (noise, kids, guests)
- Discourage rough play and activity
- Provide a warm and comforting environment
- Hire an experienced dog sitter to monitor your dog while you are away
- Track your dog’s appetite, drinking, urination, weight and behavior
- Be consistent when it comes to dieting regimen and pain meds administration.
Last but not least, start end-of-life discussions with reputable euthanasia services in your area. These discussions, although extremely painful, must be started before your dog’s quality of life declines significantly and before the pain becomes unmanageable.
Prognosis for Dogs With Osteosarcoma
In general, prognosis is substantially worse if there is proof of tumor spread that's actually visible on chest radiographs under the form of nodules. However, even with clean x-rays, it's important to recognize that there is usually still spread, only that it's just not big enough to pick up yet.
The average survival time without treatment is generally around 2 months. For dogs with limb amputation the average survival time is prolonged to about 6.5 months.
For dogs subdued to palliative radiation and chemotherapy, the average survival time is 6 months. Dogs that had the affected limb amputated and then received chemotherapy, are likely to have average survival times of around 1 year. The prognosis is usually the same for dogs undergoing limb-conserving surgery and chemotherapy.
Simply put, either with or without treatment, the prognosis for dogs with osteosarcoma remains guarded to grave.
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About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.
She currently practices as a veterinarian in Bitola and is completing her postgraduate studies in the Pathology of Domestic Carnivores at the Faculty of Veterinary Medicine in Zagreb, Croatia.
Ivana’s research has been published in international journals, and she regularly attends international veterinary conferences.