Dog Osteosarcoma – OSA
Canine Osteosarcoma accounts for 80% of malignant bone tumors and usually affects the leg bones of middle-aged or elderly dogs with a mean age of 1 ½ years. Appendicular osteosarcoma develops within the bone in the metaphyses of long bones of forelimbs, distal ulna, proximal and distal tibia and femur. Factors include ionizing radiation, chemical cardinogens, foreigt bodies and pre-existing skeletal abnormalities. This tumor metastasizes through hematogenous routes. Common sites include the lung, liver, kidneys and amputation stumps.
The rapidly growing tumor wreaks destruction from the inside out. Canines experience progressive pain and lameness. Normal bone is replaced by weaker tumorous bone that can break with minor injury. A pathologic fracture may indicate the bone tumor.
Breeds affected by Canine Osteosarcoma include Saint Bernards, Rottweilers, Great Danes, Golden Retrievers, Irish Setters, Doberman Pinschers and Labrador Retrievers. Family lines may indicate a genetic disposition.
Symptoms and Diagnosis
Symptoms of OSA include lameness, swelling and pain. Edema and reactive fibroplasias may cause soft tissue swelling. As the tumor expands, other signs include edema, fibroplasia, and periosteal new bone formation. Subsequent pathologic fractures may indicate the tumor has weakened the cortical bone.
Diagnosis through radiographs and biopsy can evaluate persistent lameness. Primary bone neoplasm may be lytic, productive or mixed appearance. A lytic lesion shows area of bone that has been destroyed. A sunburst pattern or corona effect indicates the tumor growing outward and pressuring normal outer bone up and away. A fracture may show through abnormal bone.
A biopsy involves a tiny section of bone. When in doubt about a lesion on an x-ray, a vet can perform a bone biopsy for specific results. If inflammation surrounds a bone tumor, several samples may be taken.
Treatment of OSA may include surgery, chemotherapy and radiation therapy. Without treatment, a canine may survive for two to six months.
Amputation of affected bone is a palliative approach that resolves pain in 100% of cases. The dog can run and play with no restriction. Unlike humans concerned with body image, canines feel no disfigurement.
Limb sparing surgery works well for tumors of the distal radius. Removing the tumorous bone and replacing with a bone graft allows for regrowth through ‘bone transport osteogenesis.’ The joint nearest the tumor is fused. If a tumor affects more than 50% of the bone or adjacent muscle, this procedure would not likely be performed. Complications to consider include bone infection, implant failure and tumor recurrence and fracture.
Treatment of cancer through chemotherapy after amputation may control the disease and increase survival time. Younger dogs may experience more aggressive disease and shorter survival times than older counterparts. Chemotherapy protocol includes cisplatin, carboplatin, doxorubicin, and a combination of doxorubicin and cisplatin. Without chemotherapy the median survival time is four to five months from diagnosis, with or without amputation.
Radiotherapy can control pain and improve limb function with first three weeks and lasts four months. This treatment fails to help one-third of patients. With pain relief, increased physical activity may result in bone fracture.