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So What is Cancer?

Cancer, Osteosarcoma in our Pets

When cells are disrupted due to genetic makeup, trauma, a virus, bacteria, fungus, inflammation, solar exposure, etc. they can begin to rapidly divide and act erratically compared to their normal defined behavior. When this happens the rapidly dividing cells can grow and create a tumor or spread and invade other tissues. This leads to distant metastatic tumors that disrupt those tissues creating pain, inflammation, and poor function of the affected organs.
All of us have either had a bout with cancer or experienced a loved one or friend that has had the disease. Our furry friends also can be afflicted by cancer. So I wanted to discuss cancer in our pets so people can be more aware of it and how it presents clinically in one specific common cancer, osteosarcoma.
What is Osteosarcoma?
At this time we don’t know the cause of osteosarcoma but we know it is mostly seen in large breed dogs often involving the long bones such as the humerus, radius, and femur. Like many cancers, it is seen in older dogs but can be seen infrequently in young pets too. Less often we will see it in the axial skeleton involving bones in the spine, pelvis, and skull. I have personally seen an 18 month old Visla with severe osteosarcoma in the femur.
How can I tell if my dog has Osteosarcoma?
Often, we see owners complain of their dog limping suddenly with or without a swollen limb. The most common areas are the distal femur and proximal tibia and proximal humerus and distal radius. Of course, we explore other reasons for lameness such as a cranial cruciate tears, bone infection, fungal infection, bone cyst, etc when working up a lameness case. Radiographs often will reveal or give us a suspicion of osteosarcoma. I have included a radiograph showing an aggressive lesion in the radius in Figure 1. Some lesions are very aggressive while others are more subtle and may be revealed with subsequent radiographs in 2-4

weeks. Often we perform 3 view chest radiographs looking for metastatic lesions. It is an important part of giving an accurate prognosis for clients. Lesions in the chest carry a more grave outlook. Advanced imaging (CT) is about 80 x more sensitive at findings metastatic lesions than radiographs if an owner is OK ending the extra money for this testing. Bone biopsy is the next step either with a Jamshidi bone core biopsy instrument or an open routine surgical approach. I always let owners know that the results may be inconclusive or nondiagnostic, the procedure will lead to some more pain in the short run, and will increase the chance of pathologic fracture. Sometimes pets will present with a pathologic fracture which is where the bone is already fractured from the cancer.
How is it treated?
Unfortunately, amputation is part of the treatment of choice with osteosarcoma. The bad news is that median survival time is 4 months and less than 10% of dogs live for one year with most often dying from metastatic lesions in the lungs.
A more expensive option is limb sparing surgery where a surgeon removes the cancerous part of the bone and inserts healthy bone. However, the data shows this has similar survival time to amputation.
Now if chemotherapy is added after surgery the median survival time jumps to 10-12 months with as many as 20% living for 2 years. The most common drug used to be Cisplatin but is wrought with some major kidney damage and vomiting side effects. It has been replaced with Carboplatin as these issues are generally not seen with its use. Expect your doctor to recommend 4 treatments about 3 weeks apart with labwork to make sure organs are OK and white blood cell counts are at appropriate levels. Other chemo drugs have been tried but none to this point have been shown to be more effective.
What else effects the prognosis?
Ask your doctor at the time of surgical biopsy to include the regional lymph node. If osteosarcoma is found in the lymph node the prognosis is much worse and may effect if an owner goes through with amputation and chemotherapy. Of course, like we mentioned above, the prognosis is definitely improved with surgery and chemotherapy vs. surgery alone. The

prognosis is also better when, if metastasis is found, it is found in the bone vs. soft tissue like lung tissue. So you can see again why lymph node and bone biopsy, radiographs, and CT are so important.
What if the owner does not want surgery?
If a client absolutely does not want surgery, radiation treatment is available in several outpatient treatments for pain control. Stereotactic radiation therapy (SRT) at referral institutions is also available and some recent data suggests it and chemotherapy together may be as good or better than amputation and chemotherapy. This applies to early diagnosed cases and small lesions. There are some more exotic expensive options that may be offered at veterinary schools but are not common enough to discuss here.
Pain control at any level of treatment is very important. Many drug options are available and include NSAIDS (such as Rimadyl), Tramadol or Fentanyl patches, and Gabapentin. Unfortunately, class IV laser therapy is not recommended as it will promote blood flow to the cancer and enhance its growth.
I wanted to mention that cats can develop this disease too but is much less common. Aggressive limb amputation can often result in long term survival. Axial skeleton involvement (spine, pelvis, skull) is more commonly involved than in dogs. We recently saw a cat with an aggressive lesion in the jaw and I have included a radiograph of this lesion here. (Figure 2).
Unfortunately, osteosarcoma is an aggressive disease that we can’t cure but we can often extend our pets’ lives giving us more precious time with our best friends. I will always recommend routine exams for people’s pets and every 6 month exams on senior dogs. The key is for owners to do a physical exam on their pets every week. Have your vet show you where to check for enlarged lymph nodes and the most common sites to check for bone lesions on your pet. As soon as you see something that does not seem right (lameness, mass, swollen leg), check with your vet. Just like cancer in people, early diagnosis give you more options and likely more time with your furry friend.

Dr. Timothy Warner

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