Introduction

• 3-5% of all canine tumors.
• Incidence rate of 27.2 dogs per 100,000, however this depends on breed and specific country population.
• Cause: lameness, bony swelling.
• Diagnosis: clinical signs, radiography, histopathology.
• Treatment: surgery +/- chemotherapy.
• Prognosis: good for benign lesions, guarded for malignant, however 90% of bone tumors are histologically malignant.
• Most common tumor is osteosarcoma, however multilobular osteochondrosarcoma, chondrosarcoama, fibrosarcoma and hemangiosarcoma are reported.
• Metastases from other tumors, especially carcinoma of the urinary tract and mammary carcinoma.
• Metastases of appendicular osteosarcoma and rib osteosarcoma are very common. Axial osteosarcoma carries a significant low metastatic rate compared to appendicular, but delayed metastases later than one year after diagnosis can occur. Axial osteosarcoma tend to be more locally aggressive and the control of the local disease is more difficult.

Pathogenesis

Etiology

Primary

• Osteosarcoma Osteosarcoma (>90% of all bone tumors).
• Multilobular osteochondrosarcoma (MLO).
• Fibrosarcoma (FSA) Fibrosarcoma (<10% of all bone tumors).
• Chondrosarcoma Chondrosarcoma, more common in nasal cavity and rib.
• Hemangiosarcoma Hemangiosarcoma.
• Multiple myeloma Myeloma.
• Lymphoma Lymphoma.

Secondary

• Metastasis or local invasion from soft tissue or bone tumors.
  • Adenocarcinoma Adenoma-adenocarcinoma (mammary Mammary gland: neoplasia, prostatic Prostate: neoplasia, bladder Bladder: neoplasia, pulmonary Lung: pulmonary neoplasia).
  • Transitional cell carcinoma.
  • Melanoma (oral) Melanoma.
  • Lymphosarcoma.

​​Local invasion

• Other tumors invading bone locally, eg oral melanoma, SCC Skin: squamous cell carcinoma, fibrosarcoma.
• In appendicular location, articular/periarticular histiocytic sarcoma Skin: histiocytoma can invade joint and bones. Rarely high grade subcutaneous STS Soft tissue sarcoma can invade the bone. Synovial cell sarcoma Synovial cell sarcoma can extend from the joint to invade bones.
• See individual components for further information.

Pathophysiology

• Etiology unknown, however micro-trauma/fractures in large breed dog could be potential contributing factors in a predisposed genetic background. Metal implants, osteomyelitis Osteomyelitis and fractures potential contributors of neoplastic transformations.
• Malignant transformation of cells within bone (osteoblasts, chondroblasts, osteoclasts, etc)  →   uncontrolled proliferation and production of matrix (osteoid or chondroid).
• Destruction of normal bone  →  lysis and possibly pathological fracture.
• Metastasis common in appendicular and rib, less common in other axial locations.
• Benign lesions are very rare and show less disorganization of normal bone structure. Bone cyst can appear clinically as a swelling, etiology is unclear.

• Disruption of normal bone structure by cellular proliferation, matrix production and bone destruction causes periosteal reaction, pain and bony swellings.
• Reduced weight bearing in limbs and therefore lameness.
• Surrounding tissues are invaded to some extent but joint function is rarely compromised as invasion of the joint by osteosarcoma is rare.
• Extreme bone lysis in long bones may lead to pathological fracture.
• Mass affecting ribs may cause dyspnea or pleural effusion Pleural: effusion.
• Mass affecting pelvis may cause constipation.
• Mass in vertebral column may cause tetra/paraplegia.
• Sites can be appendicular or axial skeleton.

Timecourse

• Benign lesions progress slowly – months (benign lesions very rare).
• Malignant lesions progress rapidly – days to months.
• Osteosarcoma progress very rapidly - days to weeks.
• Chondrosarcoma, fibrosarcoma and multilobular osteochondrosarcoma progress much more slowly than osteosarcoma.
• Rarely low grade osteosarcoma (around 5% of cases) that can progress less rapidly is reported. Parosteal osteosarcoma is also slowly growing with lower metastatic rate.

Diagnosis

Treatment

Outcomes