Radiation Can Help Control Pain for Dogs with Osteosarcoma

Dutch, a 6 year old, neutered male Great Dane presents to his primary care veterinarian for pain. His owners report that he seems like he has been getting older and slowing down, he has trouble getting up and down stairs, and this past weekend they noticed a swelling on his left front leg. Otherwise Dutch has been doing well.

On examination there is a large firm swelling of the distal antebrachium, Dutch is moderately lame on that limb and he has difficulty rising in his back end. Radiographs of the limb are performed and a lateral view is shown in Figure 1. The radiographs show a number of “classic” signs of an aggressive bone lesion:

bone

  • Irregular new bone formation – there is smooth new bone on the proximal aspect of the lesion in the shape of a triangle, often referred to as a Codman’s triangle. Also there is a large amount of patchy irregular new bone on the cranial aspect of the limb in what looks like a “sunburst” pattern.
  • Loss of cortical detail – in the central aspect of the lesion the cortex is thinned out, consistent with bone loss.
  • Location – as solitary lesion in this location, the metaphysis of the distal radius, is highly suspicious for osteosarcoma. Other common sites are the proximal humerus, distal femur, and proximal tibia

Three-view thoracic radiographs are performed and they are normal, with no evidence of metastases. After further discussion with the owners, Dutch has no history of travel out side of the North East United States. Based on signalment and radiographic findings the lesion is thought to be most consistent with a primary bone tumor, primarily osteosarcoma and a forelimb amputation is recommended. However, after a complete orthopedic exam it is determined that Dutch also has severe hip osteoarthritis and due to his large size, an amputation is not recommended.

A fine needle aspirate is performed, revealing spindloid cells, consistent with a sarcoma.

Dutch’s owners decide to start Dutch on oral pain medications and pursue palliative radiation.  Dutch receives four radiation treatments to the distal forelimb. His owners report that two days after the first treatment Dutch starts using the leg more and they start to cut back on his pain medications.

Background
Osteosarcoma is the most common bone tumor in dogs. Duke’s signalment and presentation are common – an aggressive bone lesion in the metaphyseal region of the long bones in a giant breed dog.

The ideal recommendation for treatment is surgical excision of the tumor, usually by amputation, followed by a course of chemotherapy. Survival times with surgery alone are approximately 4-6 months (Spodnick et al JAVMA 1992). Chemotherapy more than doubles this with average reported survival times of 12 months with 10 – 20 % of patients surviving 2 years or more (Withrow, Vail 2007)

In cases where an amputation may not be the ideal recommendation, palliative radiation therapy has been shown to be a very effective treatment option to provide pain control for the local tumor in 75 to >90% of dogs (Ramirez et al Vet Radiol Ultrasound, 1999; Green JAAHA 2002) Palliative radiation therapy usually involves between two and six treatments, delivered over one to three weeks. Side effects are typically very minimal, with mild irritation of the local skin. Pain control can occur within 48 hours and typically will happen within one week (Green JAAHA 2002).

Other palliative options include bisphosphonates, such as pamidronate. While less successful than radiation in controlling pain for bone tumors, they have been shown to have some benefit also with minimal side effects (Fan et al JVIM 2007). Also, the addition of pain medications and/or bisphosphonates to a course of radiation may result in significant pain control, although these types of combination treatments have not been fully investigated.

John Farrelly, DVM, MS , ACVIM (Oncology), ACVR (Radiation Oncology)
The Veterinary Cancer Center

References
Spodnick GJ, Berg J, Rand WM, et al. Prognosis for dogs with appendicular osteosarcoma treated by amputation alone: 162 cases (1978-1988).J Am Vet Med Assoc. 1992 Apr 1;200(7):995-9.
Dernell WS, Ehrhart NP, Straw RC, Vail DM Tumors of the Skeletal System in Withrow and MacEwen’s Small Animal Clinical Oncology, 4th Ed. Saunders, St Louis Missouri 2007 pp. 559 – 563.
Ramirez O 3rd, Dodge RK, Page RL, et al Palliative radiotherapy of appendicular osteosarcoma in 95 dogs. Vet Radiol Ultrasound. 1999 Sep-Oct;40(5):517-22.
Green EM, Adams WM, Forrest LJ. Four fraction palliative radiotherapy for osteosarcoma in 24 dogs. J Am Anim Hosp Assoc. 2002 Sep-Oct;38(5):445-51.
Fan TM, de Lorimier LP, O’Dell-Anderson K, et al. Single-agent pamidronate for palliative therapy of canine appendicular osteosarcoma bone pain. J Vet Intern Med. 2007 May-Jun;21(3):431-9.

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