Canine Osteosarcoma

Filed Under: Dogs, Diseases

Does your dog have a swelling of the leg that is painful when touched?   Is your dog suddenly lame?  Can’t remember a traumatic incidence your pet has been subjected to recently?   Is your dog over 50 pounds in weight?  If the answer to most of these questions is yes, you should take your pet to his veterinarian.   Large and giant breeds of dogs are particularly susceptible to osteosarcoma which is a highly aggressive and malignant tumor or cancer of the bone.  Radiographs will clearly demonstrate if you have to be concerned about this type of tumor.
Osteosarcoma is the most common primary bone tumor in the dog, accounting for 85% of all primary bone tumors and 5% of all neoplasia in the dog.  The term “primary” designates the tumor’s origin in the bone - - a distinction that precludes the possibility of metastasis from a tumor that originated in another tissue.
Breeds commonly affected by osteosarcoma include the Irish wolfhound, Scottish deerhound, Saint Bernard, Labrador retriever, Borzoi, Rottweiler, Great Dane and the greyhound.  Most of these dogs are strickened when they are middle-aged and older, typically at 7 to 10 years of age.  Some researchers report an additional incidence peak at around two years of age.  Dogs that are neutered are more likely to develop osteosarcoma than are sexually intact animals.  It has been theorized that because neutered animals are more likely to be overweight they may have a greater risk of osteosarcoma development.  Male dogs are reported to be a greater risk than females with the ratio of 1.5 males for every 1 female.  Although not recorded in the literature, this author has noted that the development of osteosarcoma to be more common several years following the repair of a long bone fracture with either a bone plate or intermedullary pin.  When osteosarcoma occurs following a fracture repair it does not occur with the same breed specificity seen under normal circumstances.  
The site of osteosarcoma development often correlates with the particular breed of dog affected.  Rottweilers and Great Danes are more likely to have osteosarcoma developing in the forelimbs rather than the hindlimbs.  In these two breeds, the proximal end of the humerus and the distal end of the radius are the most common sites of tumor development.  In the greyhound the proximal end of the femur is the most popular area for the development of osteosarcoma.  In general, it is the metaphyseal region (the wider part of the extremity of long bones that contains the growth plate in young animals) of the long bones in the forelimbs and hindlimbs that is the most common site of osteosarcoma development. 
In the greyhound osteosarcoma is particularly aggressive: even more so than what is seen in other breeds of dogs.  Osteosarcoma is the most common cause of death in retired racing greyhounds and is reportedly involved in 25% of all deaths in these animals.  In direct comparison, osteosarcoma is rarely seen in AKC registered greyhounds.  It has been theorized that repetitive trauma and stress on the long bones in greyhounds during their racing careers may contribute to the increased risk for osteosarcoma development.  In racing greyhounds 75% of the osteosarcoma diagnosed occurs in the front legs and 59% of all cases are reported in male dogs. 
Osteosarcoma is seen clinically as a sudden onset of lameness and/or swelling of the affected limb.  There is typically no history of trauma.  The leg is painful when palpated and may be so painful that the dog does not place any weight on the leg.  Often a fracture of the bone will be palpable or visible.   
When osteosarcoma is suspected, radiographs should be taken of the affected limb as well as views of the chest for the detection of metastatic lesions.  Most lesions found in the bone are lytic (show bone destruction), and approximately 26% of those dogs radiographed will have pathologic fractures (broken bones as a result of the abnormal bone pathology) of the affected bone upon diagnosis.  
Metastic tumors (the ability of a tumor to spread to additional body areas) with osteosarcoma occur in 80% to 90% of all cases.  Pulmonary metastatisis is seen radiographically as discrete soft-tissue nodules within the lungs with multiple lesions being common.  Other common sites of metastatisis include the skin or additional bones. 
Osteosarcoma may be confused with osteomyelitis, which is a bacterial or fungal infection of the bone, other metastatic bone tumors or less common diseases of the long bones such as multiple myeloma or lymphoma.  Diagnosis of osteosarcoma is typically confirmed by biopsy although fine-needle aspiration may be confirmatory in certain incidences. 
The treatment of choice for osteosarcoma is limb amputation followed by adjuvant chemotherapy.  Chemotherapy protocols typically incorporate carboplatin, doxorubicin or suramin/doxorubicin.   An actual cure occurs in less than 10% of canine patients suffering with osteosarcoma even with intensive treatment.  Typical survival time is approximately 1 year following diagnosis with most patients succumbing to pulmonary metastatic disease. 
Radiation therapy has been used as a palliative treatment for bone pain.  Radiation is usually given on a weekly interval for 2 to 4 consecutive treatments.  When no treatment is given, most owners will elect euthanasia within 2 months of diagnosis. 
A promising new treatment is under study that may delay metastasis of osteosarcoma.  Rapamycin, a bacterial macrolide produced by Streptomyces hygroscopicus has been shown to have immunosuppressive, antiproliferative, and antitumor effects.  Current experimental studies have demonstrated that injectable rapamycin resulted in a dose-dependent decrease in the growth of osteosarcoma at a dose of 0.05 mg/kg/d.

Bonagura, John and David Twedt Editors.  Kirk’s Current Veterinary Therapy XIV.  Saunders/Elsevier.  2009.   Pp. 358-362.
Couto, C. Guillermo.  “Greyhound Bone Cancer.”  NAVC Clinician’s Brief.  July 2008. P. 37.
Dimopoulou, M., J Kirpensteijn and H. Moens et al. “Histologic Prognosticators in Feline Osteosarcoma:  a Comparison with Phenotypically similar Canine Osteosarcoma.” Veterinary Surgery 2008; 37 (5):  466-471.
Gordon, Ira and Fang, Ye et al.  “Evaluation of the Mammalian target of Rapamycin Pathway and the effect of Rapamycin on target expression and cellular proliferation in Osteosarcoma cells from Dogs.”  AJVR, Vol 69, No. 8, August 2008. Pp. 1079-1083.
Rosenberger, Julie and Norma Pablo, et al.  “Prevalence of and intrinsic Risk Factors for Appendicular Osteosarcoma in Dogs:  179 cases (1996-2005).  JAVMA, Vol. 231, No. 7, October 1, 2007. Pp. 1076-1080.

Topics: bone disease, bones, cancer, greyhounds, tumors

Symptoms: lameness, swelling

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