Owen Davies is a 2005 Cambridge University graduate. He had extensive experience in general practice, including small and large animal, over a period of ten years or so. He obtained his specialist qualifications after a residency at the Royal Veterinary College. Since 2017 he has worked at Highcroft Referrals in Bristol.

Owen begins this veterinary webinar with a brief introduction to the typical presentation of bone tumours, followed by a more general classification as aggressive bone lesions. Features such as bone lysis, periosteal reaction and transition zones are described and radiographic images of dogs and cats are seen.

A series of key points occur throughout the webinar.

 Key point  

  1. You can demonstrate an aggressive bone lesion radiographically using some/all of the following features: 
  • Permeative /moth -eaten cortical lysis
  • Long transition zone
  • Irregular periosteal reaction
  1. The degree of radiographic aggression doesn’t correlate with clinical aggression
  2. Absence of aggressive features makes clinical aggression unlikely

There are a surprisingly large number of diseases to be considered in the differential diagnosis of aggressive bone lesions in dogs, (12 in all). These are listed under the general headings of bacterial and fungal osteomyelitis, primary bone tumours, tumours of bone marrow origin and metastases to the bone.

Treatments and prognoses differ, emphasising the need for an accurate diagnosis.

In order to help in making a diagnosis consideration is given to the travel history and life style, the breed and the anatomic location. As is entirely expected, the webinar contains a large number of very high quality radiographic images and the next part illustrates diaphyseal haemangiosarcoma, histiocytic sarcoma, and multilobular osteochondrosarcoma.

The differential diagnosis in cats is less extensive but a warning is given of the existence of mycobacterial disease, and also that up to 90% of bone tumours in this species are malignant.

Encouragingly Owen advises that for diagnosis fine needle aspirates are usually all you need. Some excellent ultrasound images show how ultrasound can indicate optimal sites for FNA sampling, and cytological images of osteosarcoma, histiocytic sarcoma and lymphoma are shown. There is general advice on cytological and bone biopsy sampling.

Key point

  1. An aggressive lesion can have multiple diagnoses-and sampling is needed
  2. Signalment and anatomic location and presentation can help refine diagnoses
  3. FNA is adequate in most cases
  4. A biopsy is sometimes necessary
  5. Beware of zoonotic disease-especially in cats

After this general introduction there is more specific information on osteosarcoma in dogs. It is the most common primary bone tumour in this species. There is some interesting background statistics on relative risks according to breed and size of the dog and also the sites more commonly affected. A series of radiographs, CT images, 3D reconstructions and clinical images summarise these.

Key point

Osteosarcomas of different locations vary in their aggression but they all have a strong metastatic propensity and staging is indicated.

  • In staging, lungs are the predominant site for osteosarcoma metastasis
  • 90% of cases will develop metastasis in the first year of treatment
  • Bone (5%) and Lymph node (19%) involvement have been reported
  • 80% of pulmonary nodules detected on CT scan are not visible on radiographs

Key point

  • Staging involves imaging of thorax and abdomen (+/-) bones
  • Radiography of thorax and abdominal ultrasound?
  • CT of thorax and abdomen is much more accurate than radiology, detecting 2mm versus 6-7 mm nodules, plus better bone and soft tissue detail
  • But is this information going to change things?

The webinar moves on to treatment, which is divided into local and systemic therapy. For local therapy amputation is the treatment of choice in most cases, associated as the only treatment with 3-5 months survival, and there is some surgical information on techniques. There are some heart-warming videos of three legged dogs playing and obviously enjoying life-worth showing to owners unsure of the benefits of amputation.

Surgical limb spare is another option briefly described. There are some limb spare complications, such as tumour recurrence, infection, pathological fracture, plate breakage and loosening of the implant. Overall, Owen’s opinion is that the procedure, except in a few listed situations, is of limited benefit or inappropriate for most dogs.

Other local therapies discussed include: – stereotactic radiation therapy, analgesia for non-surgical cases, and also the possible use of bedinvetmab, (Librela), palliative radiation therapy and cementoplasty

Key point

  • If an osteosarcoma remains in situ every effort should be made to ensure the patient remains comfortable and their welfare should be carefully monitored
  • Multiple oral analgesic drugs are rarely sufficient-consider radiotherapy or biphosponates?

The next part of the webinar is entitled ‘Controlling Metastasis-Chemotherapy’. There is a detailed description of the use of carboplatin, doxorubicin, cyclophosphamide, toceranib/piroxicam, adjuvant sirolimus, and immunotherapy with a HER2-Targeting Listeria. The next key point simplifies matters, however: 

Key point

Currently the standard-of care adjunctive chemotherapy for canine osteosarcoma is 4-6 injections of carboplatin (or doxorubicin) starting 14 days after surgery

For monitoring and changing treatment restaging every 3-6 months is suggested (or when thinking of changing therapy.) We are reminded that no treatment will be 100% effective or that responses to therapy will last.  Intervention should be considered when metastasis starts to develop and the goal of treatment is to retard the development of these lesions. There is a description of the ‘RECIST’ Criteria (Response Evaluation in Solid Tumours) with additional information on second-line therapy, before a discussion on palliative care in the final stages of the disease. A possible sequel of metastatic osteosarcoma is Hypertrophic Osteopathy, which is described with some striking clinical cases.

Key point

  • The key to a good outcome is monitoring, restaging and adapting the treatment based on progression of disease and associated clinical signs

The next part of the webinar gives prognostic statistics for non-metastatic appendicular osteosarcoma. Limb amputation alone, palliative radiation therapy alone, palliative radiotherapy and chemotherapy have a relatively disappointing prognosis of 3-5 months. Limb amputation and chemotherapy achieves a much improved 10-14 months with 25% of dogs alive at 24 months.

Similar prognostic statistics are given for cases that are metastatic at diagnosis, and for the other osteosarcoma sites, together with other useful prognostic information such as haematological and serum biochemical values, tumour grade, histological sub-types and the age of affected dogs. Finally there is a brief description of feline osteosarcoma with information on site, metastatic rate and prognosis. Adjuvant chemotherapy is not indicated

The summary is detailed and included here in full

  1. Many differentials for an aggressive bone lesion are available. These have very different treatments
  2. Use signalment and anatomic location to refine the differentials and FNA will give you a diagnosis in the majority of cases
  3. Osteosarcoma requires local therapy for pain control but medical therapy to control metastatic disease
  4. Amputation remains the mainstay for local therapy for pain control but medical therapy to control metastatic disease
  5. A dog with a typical distal radial osteosarcoma can expect to survive 10-14 months with surgery and amputation
  6. Carboplatin and doxorubicin are the most effective chemotherapeutic agents. The benefit of maintenance therapy has not yet been proven but the benefit of frequent restaging and adapting your treatment to the patient is clear
  7. Consider multi-modal analgesia, radiotherapy and bisphosphonates for palliative cases
  8. Osteosarcoma lesions in cats can look deceptively non-aggressive, has fewer differentials and is less metastatic. The benefits of chemotherapy has not yet been shown

This is an extraordinarily well-researched webinar with an abundance of clinical material including imaging.  It is a comprehensive update on canine osteosarcoma, with information of value to first opinion colleagues when discussing cases with owners, and whether to refer to a specialist. For specialists it is also a very good summary of current thinking with good links to the latest literature.