Bone tumors either involve the appendicular (limbs) or axial (spine, ribs, pelvis, scapula, and skull) skeleton, said the American College of Veterinary Surgeons (ACVS), an agency that defines the standards of surgical excellence in veterinary medicine. The tumors are categorized as primary or those that arise directly in the bone or secondary, meaning the tumors spread from an adjacent site like multiple myeloma of the bone marrow. There are four primary bone tumors: osteosarcoma, chondrosarcoma, fibrosarcoma, and hemangiosarcoma.
The most common tumor is osteosarcoma, representing over 95% of all tumors. In canines, appendicular osteosarcoma is an aggressive disease and treatment involves surgical resection of the tumor along with chemotherapy. These options reduce the risk of tumors metastasizing or spreading to other areas, especially in the lungs and other bones. Tumors can also manifest at sites of previous bone damage. Bone damage such as fractures and total hip replacement is associated with the development of primary bone tumors. However, the risk of developing a bone tumor after fracture etc. is rare as most primary bone tumors develop spontaneously with no predisposing cause.
Breed-Specific Incidence Rates of Canine Primary Bone Tumors In Dogs In Norway (2011)
Kristin P. Anfinsen and colleagues of biomedical and life sciences journal PMC found that 43 dogs met the criteria for positive of primary bone tumors. The diagnosis was based on clinical examination and x-rays, with a lifetime risk of 2.3% (1.6% to 3.0%). Of these, the tumors of six dogs were biopsied. From there, the results of four canines could be obtained. Three of the biopsies resulted in OS (Osteosarcoma) and one was diagnosed as a multilobular osteochondrosarcoma.
The latter was reported in a male NF’s (Newfoundland) frontal bone. Among 1,385 dogs whose owners responded to the first request, 2.1% of dogs suffered from primary bone tumors. 2.6% of dogs among the 530 responses to the reminder were affected. The breeds with the highest incidence rates of primary bone tumors in proportion to the total number of dogs and the number of cases per 10,000 dog years at risk (DYAR) were Irish wolfhound (IW) (8.9%), Leonberger (5.8%), Newfoundland (0.9%), and Labrador Retriever (LR) (0.2%).
No significant gender differences could be observed as both male (2.4%) and female (2.1%) dogs suffered from primary bone tumors. At the time of diagnosis, the median age was 6.7 years. This was also similar with male (6.7 years) and female (6.6 years) canines. The most common sites of the primary tumor were Distal radius/ulna (35%), distal tibia (19%), and distal femur (16%). 86% of tumors came from the appendicular skeleton while 12% occurred in the axial skeleton and in the scapula, as well as in the pelvis (2.3%). 16.3% of neutered dogs were with primary bone tumors, which was similar to those not diagnosed with primary bone tumors (13.1%).
A total of 1,915 questionnaires were completed and returned to the Norwegian School of Veterinary Science (NSVS), with an overall response rate of 51%. Owners of Labrador retriever had the highest proportion of responders (53%) while Irish wolfhound was the lowest (47%).
What Are the Signs of Bone Tumors?
Symptoms of bone tumor may be non-specific and depend on the primary site, explained Penn Vet, a university founded in 1884. Tumors in the limbs often varying degrees of lameness and pain. Firm swelling may be more noticeable as the tumor grows. The pain can cause your dog to exhibit aggression and irritability. It can also suffer from poor appetite, weight loss, or may cry and whimper. When your dog has bone tumors, it may be unable to sleep or exercise. On the other hand, those in non-weight-bearing bones may first appear as a solid, firm mass. Overall, the clinical signs of bone tumors vary depending on the affected underlying structures and the primary site.
How Are Bone Tumors Diagnosed?
Initial evaluation includes performing a complete physical exam, blood tests, radiographs of the primary site and the lungs, and a biopsy. An incisional biopsy is done for diagnosis only, and a small sample of the tumor is extracted to determine its specific tumor type. Meanwhile, an excisional biopsy involves the removal of the entire tumor. Unlike the incisional biopsy, excisional biopsy is used for both diagnosis and therapeutic purposes.
How Are Bone Tumors Treated?
Treatment depends on the circumstances. Your veterinarian will need to perform a complete physical exam and work-up to accurately determine the most optimal treatment plan for your pet. Regarding cases of infection, systemic therapy such as antibiotics, antifungal, or antiviral agents may provide sufficient therapy, stated NC State Veterinary Hospital, an American educational institution in Raleigh, North Carolina.
However, painful bone lesions need to be surgically removed or amputated. For metastatic tumors, treatment will depend on the nature of the primary tumor. Therapy will be utilized to treat primary bone tumors depending on the location and the extent of the disease. Therapy for primary bone tumors entails knowing the dog’s physical condition. For example, your veterinarian will gauge its ability to ambulate or find out if it has a history of arthritis. Your veterinarian will also consider the potential for metastasis, prognostic factors like elevation in blood markers, and your goals for your pet’s quality of life. Stereotactic radiation is another option that your veterinarian could consider. This option provides pain relief without the need for amputation, though there is a risk for fracture. Amputation is most frequently recommended in addressing tumors in the limbs.
Although amputation is an aggressive therapy, most patients favored this procedure as severe pain is linked with the presence of the primary lesion. This option also eliminates the risk of fracture. Prognosis for amputation is between four to five months. Additionally, chemotherapy is recommended for treating many primary bone tumors in combination with surgery and/or radiation therapy. Prognosis for surgery and chemotherapy is around 12 to 14 months with excellent pain control and quality of life. Other palliative options are aimed at relieving pain and symptoms. Examples include bisphosphonates or IV bone supportive medications and oral medications.
There are different types of bone tumors, with the most common being osteosarcoma. Treatment depends on the results of the diagnosis, ranging from amputation to chemotherapy.