Osteosarcoma in Dogs

Osteosarcoma (OSA) is the most common primary bone malignancy in dogs, accounting for approximately 85% of all skeletal tumours [1, 31]. This aggressive neoplasm arises from mesenchymal cells that produce osteoid (immature bone) and most frequently affects the appendicular skeleton (limb bones) of large and giant breed dogs. Despite decades of research and standard-of-care therapy, OSA remains a formidable disease, with median survival times of roughly 10–12 months in dogs treated with amputation and adjuvant chemotherapy [4, 40]. However, recent advances in immunotherapy, targeted drug therapy, and minimally invasive interventional techniques are reshaping the clinical landscape.

This pillar article provides a veterinary-medical deep dive into canine osteosarcoma, integrating the latest scientific evidence, regional clinical guidelines, and practical insights for veterinary professionals and dedicated pet owners.

Quick Q&A

Question: What is the first thing my vet will do if they suspect osteosarcoma in my dog?

Answer: Your veterinarian will perform a thorough physical examination and obtain radiographs (X-rays) of the affected limb to look for characteristic bone changes such as a "sunburst" periosteal reaction and lytic bone destruction. A definitive diagnosis requires a bone biopsy (e.g., core needle biopsy) or histopathology after amputation, but advanced imaging (CT or MRI) and liquid biopsy (circulating tumour DNA) are increasingly used to guide staging and treatment planning [7, 38].

Epidemiology and Signalment

Osteosarcoma shows a striking breed predisposition, with large and giant breeds, such as the Rottweiler, Greyhound, Great Dane, Saint Bernard, and Irish Wolfhound, at highest risk. A 2025 UK-wide pathology registry study identified that breeds like the Rottweiler and Giant Schnauzer also carry elevated odds for melanoma and other sarcomas but confirmed OSA as the most common bone tumour overall [29]. The Irish Wolfhound, in particular, has been shown to harbour runs of homozygosity (ROH) overlapping genomic regions associated with osteosarcoma risk [9].

Age and sex: OSA typically affects middle-aged to older dogs (median 7–10 years), though younger dogs (e.g., age 3) can also be affected, especially in predisposed breeds. There is no overwhelming sex predilection, though some studies note a slight male predominance [31].

Location: Approximately 75% of canine OSA occurs in the appendicular skeleton, with the forelimbs (especially the proximal humerus and distal radius) being more commonly affected than the hindlimbs. Axial sites (skull, ribs, vertebrae) account for the remaining cases [40, 38]. Parosteal (surface) OSA is a less aggressive subtype that often arises on the maxilla, zygoma, or mandible [20].

Aetiology and Pathogenesis

The exact cause of OSA is unknown, but several risk factors have been identified.

• Genetic predisposition: Breed-specific susceptibility points to a strong heritable component. Recent whole-genome analyses have uncovered complex structural variants, satellite DNA fragility, and extrachromosomal DNA (ecDNA) oncogene amplification in canine OSA [34]. Mutations in TP53, PI3K, NOTCH, and MAPK pathways drive tumorigenesis and metastasis [33].
• Prior bone injury: There is preliminary evidence that dogs with a history of tibial plateau levelling osteotomy (TPLO) may have a 40‑fold increased risk of developing OSA at the surgical site, though the confidence interval is wide and the absolute risk remains low [22].
• Surgical foreign bodies: Retained surgical sponges (gossypibomas) can, rarely, induce an extraskeletal osteosarcoma (ESOSA) years after surgery, as reported in cases of gossypiboma-associated sarcoma in dogs [32, 17].

Clinical Presentation

The classic presentation is progressive, weight-bearing lameness of the affected limb, often accompanied by a firm, painful swelling at the metaphysis. The lameness may initially respond to non-steroidal anti-inflammatory drugs, but it quickly worsens as the tumour destroys cortical bone and stimulates periosteal reaction.

• Pain and fracture: Many dogs are first presented after a pathological fracture occurs through the weakened bone. In such cases, the fracture will not heal normally because of the underlying malignancy.
• Axial OSA: Tumours of the skull or jaw may cause facial swelling, exophthalmos, or difficulty eating. Parosteal OSA of the maxillofacial region often presents with exophthalmos in 40% of dogs [20].
• Intravascular OSA: Rarely, OSA can arise within the vertebral venous plexus and cause myelopathy, as described in a Standard Poodle with cervical intravascular osteosarcoma [11].
• Extraskeletal OSA: ESOSA may present as an abdominal mass (e.g., associated with a retained sponge) or a subcutaneous mass with no bone involvement [17, 3].

Diagnosis and Staging

A definitive diagnosis rests on histopathology or cytology, but clinical staging is critical to determine the extent of local disease and rule out metastasis (most commonly to the lungs and other bones).

Imaging

• Radiography: Survey radiographs of the affected limb reveal a mixed lytic-proliferative lesion with “sunburst” periosteal reaction, Codman’s triangle, and cortical destruction. However, radiographs often underestimate intramedullary tumour extension.
• Computed tomography (CT): CT is the standard for evaluating bone destruction and for thoracic imaging to detect pulmonary metastases. It is also used for surgical planning and stereotactic body radiation therapy (SBRT) target volume delineation.
• Magnetic resonance imaging (MRI): MRI provides superior soft-tissue contrast and delineates the intramedullary “transition zone.” On T2 short-tau inversion recovery (STIR) sequences, the maximal longitudinal tumour extent is significantly larger than on CT, making MRI essential for planning limb-sparing surgery or radiation fields [38]. CT-MRI fusion has been used successfully for precision radiotherapy of maxillofacial OSA [14].
• Near-infrared fluorescence imaging: A cathepsin-targeted activatable probe (VGT‑309) can be used intraoperatively to visualize viable tumour margins, aiding complete resection [35].

Biopsy

Core needle biopsy from the centre of the lesion is preferred. Histologically, OSA is characterized by malignant mesenchymal cells producing osteoid. Immunohistochemistry for the transcription factor osterix (Osx) is highly sensitive (92.5%) and specific (95.0%) for diagnosing canine OSA and can help differentiate it from chondrosarcoma, fibrosarcoma, and other mimics [1].

Staging and Laboratory Tests

• Thoracic CT: Three‑view CT is more sensitive than radiography for detecting small pulmonary metastases.
• Bone scan/skeletal survey: Consider for detecting skip or distant bone metastases.
• Complete blood count and serum chemistry: Elevated serum alkaline phosphatase (ALP) is an independent negative prognostic factor [26].
• Liquid biopsy: Circulating tumour DNA (ctDNA) analysis from plasma shows promise for monitoring disease burden and detecting early relapse. Tumour fraction in ctDNA correlates with disease status in dogs with OSA [7]. Preanalytical factors such as blood draw site (jugular versus limb vein) affect metrics, with central vein sampling being superior [7].

Prognostic Factors

Several clinical and molecular features influence prognosis.

• Presence of metastasis at diagnosis: This is the strongest negative predictor of progression-free and disease-specific survival [26].
• Histologic grade: High-grade tumours (most canine OSA) have a worse prognosis.
• Serum alkaline phosphatase: Elevated ALP at diagnosis is associated with shorter survival [26].
• Immune microenvironment: High infiltration of CD206+ M2‑like macrophages in the tumour is paradoxically associated with longer survival in dogs treated surgically, mimicking the pattern seen in human OSA [37].
• Spatial transcriptomic signatures: Long-term survivors show enrichment of immune clearance pathways and co‑localization of T/NK cells with regulatory dendritic cells within the tumour microenvironment [18].
• Inflammatory indices: In humans, neutrophil-to-lymphocyte ratio and other indices are prognostic, but a recent veterinary study found that these values were not independently associated with outcome in canine appendicular OSA [26].

Treatment

Standard of Care: Surgery and Adjuvant Chemotherapy

The current gold standard for appendicular OSA without detectable metastasis is amputation of the affected limb followed by adjuvant carboplatin chemotherapy [40]. Amputation provides immediate pain relief and eliminates the primary lesion. Most dogs adapt well to tripod locomotion, especially if they do not have pre-existing orthopedic or neurologic disease.

• Amputation techniques: For the forelimb, anterior quarter amputation (scapulectomy) or shoulder disarticulation; for the hindlimb, hip disarticulation or hemipelvectomy [40]. Meticulous surgical technique minimizes complications.

• Adjuvant chemotherapy: Carboplatin (300 mg/m² every 3 weeks for 4–6 cycles) is the most commonly used agent, extending median survival from approximately 4–5 months (surgery alone) to 10–12 months. Doxorubicin and combination protocols are also employed [28].

Limb-Sparing Surgery

Limb preservation is an option for highly selected patients with amenable tumour location (e.g., distal radius), no neurovascular invasion, and committed owners. Techniques include:

• Cortical allograft or metal endoprosthesis reconstruction following en bloc resection.
• Ulnar roll‑over transposition for distal radial tumours.
• Pasteurized autograft and bone transport distraction osteogenesis.
• Endoexoprosthesis (custom metal implant combined with a cemented stem).

A comprehensive review of surgical limb-sparing options was published in Frontiers in Veterinary Science in 2025 [36]. Complication rates, especially infection and implant failure, remain high but are acceptable in appropriately counselled clients.

Radiation Therapy

• Palliative radiation: Hypofractionated protocols (e.g., 4 × 8 Gy or 3 × 10 Gy) provide pain relief in 70–80% of dogs for 2–4 months, often used when amputation is not elected.
• Stereotactic body radiation therapy (SBRT): SBRT delivers high‑dose, conformal radiation in 1–3 fractions. It achieves excellent local control but carries a high risk of pathologic fracture (41–80%) that often necessitates subsequent amputation [6]. Prophylactic bone stabilization using the IlluminOss photodynamic bone stabilization system has been investigated as an adjunct to reduce fracture risk, though median survival in one series was only 156 days [6].
• Combined modality: A pilot study combining palliative radiation with Listeria monocytogenes-based immunotherapy (Lm‑LLO‑HER2) showed delayed primary tumour progression and prolonged overall survival in 5/15 dogs [5].

Emerging and Interventional Therapies

• Percutaneous cementoplasty: Injection of calcium phosphate bone cement into the tumour cavity after curettage provided early pain relief and improved weight‑bearing in a prospective study of 10 dogs, serving as a palliative limb‑sparing option [2].
• Histotripsy: Non‑invasive focused ultrasound ablation has been used to treat large volumes of canine OSA in a fractionated manner, reducing pain and preserving limb function in 4/6 dogs with long-term follow‑up [25].
• Cannabidiol (CBD): Preclinical studies demonstrate antiproliferative and proapoptotic effects in canine OSA cell lines, but no clinical trials in dogs are yet available [8].
• Targeted drug therapy: A phenotypic screen of 12 targeted agents at clinically relevant exposures identified alisertib, crizotinib, onvansertib, and sorafenib as active against canine and human OSA cell lines [19].
• Immunotherapy: Adoptive cell transfer using tumour‑infiltrating lymphocytes (TILs) is feasible in dogs with OSA, and functional TIL products can be expanded and exhibit MHC‑class‑I‑dependent reactivity [12].
• Low‑dose naltrexone (LDN): An oral compounded formulation improved quality of life in a small case series of dogs with various cancers, including osteosarcoma [27].
• Therapeutic delivery: Pt(IV)‑deferoxamine complexes labeled with gallium‑68 have been designed as theranostic agents for imaging and treating osteosarcoma [39].

Management of Metastatic Disease

Pulmonary metastases are the leading cause of death. A recent case report described a dog with progressive pulmonary metastases that showed a remarkable radiographic response to a triple combination of carboplatin, high‑dose losartan, and toceranib for nine weeks, but the dog eventually relapsed [28]. This approach highlights the evolving concept of modulating the tumour microenvironment (TME) to enhance chemosensitivity.

Prognosis and Survival

Despite aggressive multimodality therapy, the prognosis for canine OSA remains guarded.

• Appendicular OSA treated with amputation + carboplatin: Median survival 270–365 days; 1‑year survival rate approximately 50%; less than 20% survive 2 years.
• Axial OSA: Prognosis is more variable. Parosteal OSA of the maxillofacial region has a 1‑year survival rate of 60% with adequate surgical excision [20].
• Extraskeletal OSA: Generally very poor, with rapid progression to metastasis [17, 32].
• Emerging therapies: Immune‑based and targeted approaches are showing promise in extending survival in a subset of patients, but larger clinical trials are needed.

Prevention and Surveillance

There is no known method to prevent sporadic OSA. However, awareness of breed risk and prompt investigation of any persistent lameness in a large‑breed dog is essential. For dogs that have undergone limb‑sparing or SBRT, serial imaging (CT or MRI) is recommended to detect local recurrence or pathological fracture early. Liquid biopsy using ctDNA is a promising non‑invasive tool for monitoring minimal residual disease and predicting relapse before clinical signs appear [7].

Conclusions

Canine osteosarcoma is a highly aggressive bone tumour that remains a clinical challenge. Standard therapy (amputation and carboplatin) offers a reasonable median survival, but outcomes have plateaued. The past five years have seen remarkable progress in our understanding of the genomic landscape of OSA, including satellite DNA instability, ecDNA amplification, and immune microenvironment heterogeneity. Innovations such as histotripsy, photodynamic bone stabilization, immunotherapy (including TIL therapy and Listeria-based vaccines), and targeted molecular glue degraders are now entering clinical translation. The dog remains an invaluable spontaneous model for human paediatric osteosarcoma, and cross‑species collaboration will accelerate therapeutic breakthroughs for both species.

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