Bo: a case study on canine osteosarcoma
The case study presented here is an example of how diagnostics and therapeutics can be used in the management of a cancer patient. The case study is not intended to be prescriptive or to imply that the approach taken here is the only way to manage an osteosarcoma patient, nor is it intended to be used as a diagnostic guide. The case history includes the rationale for “decision points,” the interventions the veterinarian would make in appropriately treating the patient.
A 9 yr old neutered male Lab mix named Bo presents with a two-month history of mild lameness in the right front limb. Bo is an outside farm dog from rural Tennessee. He was seen by another veterinarian 1 month ago and placed on a nonsteroidal anti-inflammatory drug for 2 wk. The owners did not see any improvement.
On physical exam, Bo has a body condition score of 4/9. He has a grade 2/4 lameness in the right front limb and is mildly painful over the right carpus with no visible swelling. Distal limb radiographs reveal an osteolytic and proliferative lesion of the distal carpus. The lesion does not cross the joint. Three-view thoracic radiographs reveal no visible lesions and are considered normal.
Decision point rationale: Approximately 8% of dogs with osteosarcoma (OSA) have visible metastasis on radiographs at diagnosis. Diseases on the differential list are a metastatic bone tumor and infectious disease (bacterial, fungal). These considerations were discussed with the owner and a fine-needle aspiration (FNA) of the lesion was recommended.
Decision point rationale: A FNA often is diagnostic and is less invasive than a bone biopsy. If the cytology is consistent with sarcoma, an alkaline phosphatase (ALP) stain may be used to confirm bony origin.
Cytology of the FNA confirms sarcoma and an ALP stain is positive. Based on these findings, the physical exam, and the patient’s history, a diagnosis of OSA is made.
The patient’s prognosis and treatment options are discussed in detail with the owner. Treatment of the local disease (primary tumor) and systemic disease (micrometastasis) is discussed. Treatment options include surgery (amputation or limb sparing), surgery and chemotherapy, referral for these procedures, referral for definitive radiation therapy, and palliative care. Palliative care includes pain management or referral for palliative radiation.
Decision point rationale: If a referral is made, follow-up care by the primary care veterinarian is appropriate. Therefore, it is important that the primary and referral veterinarians discuss postoperative care, follow-up blood work, and management of any potential side effects.
The owner elected to pursue further staging diagnostics and is considering amputation with follow-up chemotherapy.
A complete blood count, comprehensive chemistry profile, and a urinalysis are performed to rule out comorbidities. Elevated serum ALP is a negative prognostic indicator. Additional staging considerations would entail referral for a bone scan to identify other bone lesions (<10% of cases have detectable bone metastases) and abdominal ultrasound (<10% of dogs have intra-abdominal metastases). Results of Bo’s blood work and urinalysis are normal.
A forelimb amputation is performed with uneventful recovery. At the time of suture removal, carboplatin chemotherapy is initiated and given IV once every 3 wk for a total of four treatments.
Decision point rationale: There are multiple chemotherapeutic treatment options for OSA. Chemotherapeutic agents with proven efficacy include doxorubicin, cisplatin, and carboplatin. However, studies generally have not shown clear differences in outcome between the various protocols.
Following surgery Bo returned to normal activity. His quality of life improved after amputation of the forelimb and alleviation of pain. He tolerated his chemotherapy well, but required a few days of anti-emetics after two of the treatments for vomiting.
Three-view thoracic radiographs are performed every three months following completion of chemotherapy. Nine months after the last chemotherapy treatment radiographic evidence of metastasis was found. Bo is normal clinically and enjoying a good quality of life.
The primary care veterinarian discussed Bo’s prognosis with the owner, including the likely terminal nature of the metastatic OSA and scenarios for his quality of life. Because Bo currently has a good quality of life, the owners opted to begin therapy for the metastasis and Bo is placed on a tyrosine kinase inhibitor (TKI) for the management of his metastatic disease.
Decision point rationale: Cancer should be considered and treated as a chronic disease much like end-stage renal disease or heart failure. Once metastatic disease becomes clinically apparent, a realistic goal of therapy is to attempt to stabilize it or slow its progression. Metronomic chemotherapy and TKIs are both excellent considerations in this scenario. For most owners, maintaining a good quality of life is the most important consideration.
Three months later, three-view thoracic radiographs reveal that Bo’s metastatic disease has not progressed and is stable.
Bo continued to maintain a good quality of life for six months until he eventually became dyspneic. Advanced metastatic disease was documented radiographically, and the owners elected euthanasia at that time.