Osteosarcoma In Dogs
York County Community College
Introduction to Veterinary Technology
By: Amber Allisot
Osteosarcoma (OSA) accounts for up to 85% of malignancies developing in canines, making it the most common bone tumor in dogs (Belda, Lara-Garcia, & Lafuente, 2016). A sarcoma is a malignant(cancerous) tumor that develops in the connective tissues, affecting bone, and cartilage (Simpson, Grau-Roma, Rutland, de Brot, Dunning, & Mongan, 2017). While any dog can develop OSA, larger and older breeds of dogs have an increased risk. (Simpson et al., 2017). Breeds at more of a risk of developing osteosarcoma are Dobermans, German Shepherds, Golden Retrievers, Great Danes, Greyhounds, Irish Setters, Rottweilers, and Saint Bernards. (Bonagura, 2014). According to the authors Murphy, Mok, York, Rebhun, Woolard, Hilman, and Skorupski, “At the time of initial diagnoses, most affected dogs have occult pulmonary metastases. Even with aggressive surgical treatment combined with chemotherapy, the majority of dogs diagnosed with osteosarcoma live less than one year from the time of diagnosis” (2017). In this paper, I will talk about all aspects and possible outcomes related to canine osteosarcoma. I will go in depth about the symptoms of canine osteosarcoma, how it is diagnosed, different treatment options, prognosis and client compliance.
Canine osteosarcoma often presents itself in clinic with symptoms of fatigue, loss of appetite, possible pain and swelling, as well as the most common symptom, lameness (Szewczyk, Lechowski, & Zabielska, 2015). During my personal interview with Dr. Del Borgo, she agreed and stated that typical clinical signs of osteosarcoma are lameness and/or limping in the affected limb. The affected dogs tend to be older (8 years and up) and larger breeds, although she recently diagnosed a Boston Terrier (Personal communication, November 17, 2017). The appendicular skeleton tends to be favored by the disease over the axial skeleton. (Simpson et al., 2017). Within the limbs of animals contain the bones that make up the appendicular skeleton (Colville & Bassert, 2016). According to the authors Belda, Lara-Garcia, and Lafuente, “The two most common sites for osteosarcoma include metaphyseal regions of distal radius and proximal humerus” (2016). According to Del Borgo:
In the early stages of canine osteosarcoma, limping and pain on palpatation of the long bone with the cancer in it are sure symptoms. A rule of thumb about osteosarcoma is “close to the knee, away from the elbow” – so we tend to see it most commonly in the lose femur, upper tibia, upper humerus, and lower radius/ulna, but any bone can be affected. (2017)
In order to positively diagnose a dog with osteosarcoma multiple tests need to be done, a physical exam, as well as x-rays and blood work should be examined and tested (Szewczyk et al., 2015). If positively diagnosed, a biopsy can be done in order to determine the type of tumor it is (Szewczyk et al., 2015). The interior of the bone looks like Swiss cheese with cotton candy-like calcifications on the exterior of the bone (A. Del Borgo, personal communication, November 17, 2017). Unlike chondrosarcoma or fibrosarcoma, canine osteosarcoma progresses aggressively, with proven earlier lung metastasis (the development of another malignant tumor)(Murphy, Mok, York, Rebhun, Woolard, Hilman, & Skorupski, 2017). According to authors Belda, Lara-Garcia, and Lafuente, “Physical exams are essential to detect evidence of metastasis. Complete bloodworm with urinalysis including bone alkaline phosphate levels should be performed to determine the general status of the patient” (2016). A CT scan or MRI should be performed if limb-sparing surgery is being considered (Szewczyk et al., 2015). The most common sites for metastasis are lungs, bone, and lymph nodes (Belda et al., 2016).
The authors Szewczyk, Lechowski, and Zabielska say:
According to the TNM system (T-tumor, N-lymph node, M-metastasis) it is possible to differentiate three stages of the disease. Stage I includes low-grade (G1) lesion without evidence of metastasis (M0); stage II includes high-grade (G2) lesion without metastasis (M0); and stage III is lesion with metastasis disease (M1). (2015).
Metastasis by the time of diagnosis is already present in 90% of patients (Belda et al., 2016). Although the cause of canine osteosarcoma is unknown (Szewczyk et al., 2015), authors Belda, Lara-Garcia, and Lafuente stated “osteosarcoma has been associated with metallic implants used in fracture repair with chronic osteomyelitis and with fractures where no internal repair was used” (2016). Other factors like an animals sex, age, and/or body weight may also lead to the development of osteosarcoma (Szewczyk et al., 2015).
Helpful treatments have three possibilities: maintaining good-quality life during the time remaining, extending life beyond what is usually expected, or curing the condition (Pitcairn & Pitcairn, 1995, pp. 354,355). Treatment includes: surgery (limb amputation or limb-sparing surgery), radiotherapy and chemotherapy (Szewczyk et al., 2015). The quality of life for an animal after treatments such as chemotherapy, radiation, and surgery oftentimes is less than desirable, even if such treatments are successful (Pitcairn & Pitcairn, 1995, pp. 354,355). Amputation is usually the go-to procedure, depending on the stage of the cancer, which increases survival and brings pain relief, which delays euthanasia (Szewczyk et al., 2015). Limb-salvage surgery is usually done on patients with lower grade tumors. The advantage of limb-salvage surgery over amputation is that limb-salvage patients have a better return-to-function and possibly better overall quality of life over amputee patients (Simpson et al., 2017). Authors Murphy, Mok, York, Rebhun, Woolard, Hilman, and Skorupski stated “In addition to surgery, platinum-based chemotherapy alone or in combination with doxorubicin has shown to improve survival time” (2017). In dogs where surgery is not an option, painkillers should be given during the whole course of the disease, as well as frequent visits for orthopedic exams and pain assessment (Belda et al., 2016). During my personal interview with Dr. Del Borgo, regarding treatment she stated:
Treatment depends on how advanced the cancer is, and the owners wishes as far as how far to go. The longest life expectancy is less than a year, but you have to amputate the limb and do chemotherapy afterwards to achieve that – and even then, less than a year is pretty optimistic. If you go the amputation/chemotherapy route it can add up to thousands of dollars (Personal communication, November 17, 2017).
Many factors are associated with prognosis of osteosarcoma. Increased tumor size, higher tumor grade and mitotic index or anatomical location have been associated with poor prognosis (Belda et al., 2016). According to authors Murphy, Mok, York, Rebhun, Woolard, Hilman, and Skorupski, “The survival time of canine appendicular osteosarcoma with adequate control and without chemotherapy is 119-175 days with a 12 month survival rate of only 11-21%” (2017). A study done on dogs with stage III reported survival times of only 76 days (Belda et al., 2016). Patients with bone metastases had longer survival times (132 days) than those with lung (59 days) or lung and other soft tissue metastases (19 days) (Belda et al., 2016).
Del Borgo stated:
A majority of owners of dogs with osteosarcoma do not go the amputation/chemotherapy route, mostly because of the expense, but also because six months to a year is not a lot of time to make such treatments worthwhile for the dog. Some owners just do pain management for as long as the dog can be kept comfortable, then euthanize when the pain medication stops working (Personal communication, November 17, 2017).
In conclusion, despite all of the information we have on canine osteosarcoma and the resources we have available, a definite cure is still unobtainable at this time, further studies in veterinary medicine are needed. The disease is extremely aggressive and has a tendency to spread rapidly into other parts of the dog’s body. Generally the long term prognosis for the animal is poor, and because of the expense of treatment for the animal, owners tend to opt out of treatment and try to keep their companion comfortable until it is time to let them go.