Oncologist explained how to diagnose and treat this common type of canine bone cancer
Appendicular osteosarcoma is the most common malignant primary canine bone tumor and is typically found in large to giant dog breeds. When treated by amputation or tumor removal alone, median survival times (MST) do not exceed 5 months, with the majority of dogs suffering from metastatic disease.1 Craig A. Clifford DVM, MS, DACVIM (Oncology) director, BluePearl Science, stated that osteosarcoma (OSA) accounts for about 90% of appendicular bone tumors in dogs and 2% to 7% of all tumors in dogs.2 Because of how prevalent this disease is in dogs, Clifford explained how to diagnose and treat this type of cancer for attendees at the Directions in Veterinary Medicine symposium in Nashville, Tennessee.
Clifford stated that lameness and localized limb swelling are the most common complaints he gets when dealing with appendicular OSA. He recommended performing a thorough orthopedic examination to localize the source of lameness and differentiate metaphyseal pain from other common orthopedic diseases in large breed dogs, such as cranial cruciate ligament rupture and hip dysplasia.
He told attendees, “Seeing these cases first, we all know that the genetic influence of it, [we’ll see] large and giant breed dogs, come to you for lameness. Understandably so, you're not thinking osteosarcoma right off the bat. They're going to be treated supportively: some rest, some NSAIDs [nonsteroidal anti-inflammatory drugs], and then they get a little better, but then they get worse and are coming back to you. So at that point, some of the things to look at are going to be the signalment. Where are they laying? We know front legs are more common than back legs. Number 1 location is distal radius, [number] 2 is proximal humerus, and then 3 and 4 are around the knee. Finding a lameness along those areas is certainly going to increase [a potential OSA diagnosis].”
Clifford recommended using radiographs to establish a tentative diagnosis of primary bone tumor and differentiate this from other orthopedic diseases. In this radiograph, veterinary professionals will most likely see cortical lysis, the outside of the bone will have very visible bone destruction. Trabecular lysis, the structure of the inner portion of the bone, will also be seen and is quite common with OSA. The bone might be laid down in abnormal ways.
“The other thing we can see is the sunburst appearance. And for those of you who have never seen that before, it's essentially the tumor kind of invading into the soft tissue.”
A bone biopsy can be performed to confirm the diagnosis of OSA using a Jamshidi needle but is not necessarily required prior to treatment. Clifford did mention the concern with biopsy, if it’s distal radius, is that it could weaken the bone further. Clifford recommended to biopsy the center, rather than peripheral.
“The other thing that can be done and this is one I would suggest is the idea of aspirating it. We and others have published [studies] on this and aspiration gives us a high probability [of correct diagnosis],” Clifford said. “Every clinic now has ultrasound. So I think it's very easy to do.”
If the aspirate comes back inconclusive or the client decides against it, Clifford recommended using the PetDx OncoK9 liquid biopsy test.
Clifford stated that with any of these techniques and options, above all, bloodwork should be performed, a complete blood count and chemistry panel. “Alkaline phosphatase (ALP) has been shown to be one of the most powerful indicators for this disease. If it's above normal, it's associated with a poor prognosis. So you're already going to have information that helps the owner regarding their decision making while they're in your office. Something to keep in mind, running bloodwork chemistry panel to make sure that they're okay for anesthesia, but also looking at the ALP level.” Clifford also mentioned that if monocyte or lymphocyte count is above normal, some studies have shown that that was associated with a poor prognosis, as well.
Clifford also recommended sending off chest radiographs to a radiologist to double check anything that could have been missed. “An owner is not going to have a problem paying for that to have a radiologist review them because there's a lot riding on something like this, it's going to make or break the case.”
Appendicular OSA is a highly malignant tumor with more than 75% of dogs eventually succumbing to their disease because of distant metastasis.1 Oftentimes metastasis can determine whether treatment will be curative-intent or palliative. However, less than 15% of dogs have clinically detectable metastasis at the time of initial diagnosis. “If there's metastasis, it changes everything. We're no longer going to have the ability to cure this dog. Most dogs that come in with metastasis at the time of diagnosis are put to sleep in about 4 to 6 weeks. So clearly that's why the radiographs are so important beforehand.”
Curative-intended treatment will include surgery, particularly limb amputation surgery, followed by chemotherapy. Clifford stated that most dogs do well after these treatments.
“The other option is more palliative. So with palliative, we can't cure them. But what can we do is maintain or help their pain control, because the main reason a dog is put to sleep with osteosarcoma is due to pain and that's usually within about 2 months.” These palliative options include analgesia, radiation therapy, and limb amputation (without being followed by chemotherapy). All these treatment options aim at controlling pain in the patient.