bone cancer (osteosarcoma) in pets
Very few words strike fear in pet owners like the “C” word, and as far as cancers go, bone tumors are some of the worst. Osteosarcoma is the most common of those found in dogs and cats, and it most often presents in the long limb bones of large and giant breed dogs.
Less often, osteosarcoma can occur in the axial skeleton (i.e., not the long bones of the limbs), and when this happens, there is no significant breed or size predilection.
Osteosarcoma is most often diagnosed in pets between the ages of 6 to 8 years old, with another small peak of occurrence in pets who are between 18 and 24 months old.
Signs & symptoms
Bone cancer is an extremely painful condition, and limping is one of the first noticeable signs. Lameness may be mild at first, and the pain responds to non-steroidal anti-inflammatories. Over time, however, lameness progresses and eventually becomes so severe that pets are unwilling or unable to bear weight on their afflicted limb.
Because tumorous bone is weak, fractures can occur at tumor sites. These types of fractures can happen as a result of normal activity — for example, jumping off of the couch, or landing after catching a Frisbee. In these cases, the patient presents with limping and a misleading history of trauma, but actually a tumor is to blame.
Swelling at the tumor site is another common clinical sign, and generally, the area is painful to the touch. Because of the pain associated with osteosarcoma, pets with this disease tend to keep a low profile. You won’t see them up and about as often, and playtime takes a back seat to sleeping.
Your vet may suspect that your pet has osteosarcoma based on their health history and physical exam, but she’ll be even more suspicious after seeing a bony lesion on your pet’s radiograph (X-ray). The lesion will look like a bone swelling on the X-ray, and the entire area will appear less dense than the surrounding bone.
Osteosarcomas do not typically cross the joint, meaning that if your pet’s lesion is present on both sides of a joint, it’s probably not osteosarcoma. Your veterinarian may want to submit your pet’s X-ray to a radiologist for an expert’s opinion, but it’s just as likely that your vet has seen enough cases to know osteosarcoma on a radiograph when she sees it.
Diagnosis will be confirmed via a bone biopsy or a less invasive fine needle aspirate. Your veterinarian will take radiographs of the lungs to check for pulmonary metastasis, or spread of the cancer. Although up to 90 percent of patients with radiographic evidence of osteosarcoma will already have metastasis in the lungs, only about 7 percent of cases will show obvious signs on X-rays. This is because the tumors are simply too small to see early on. This important step should not be skipped, however, because evidence of metastatic disease may influence your decision to treat.
Chemotherapy following amputation can extend the survival time of dogs with osteosarcoma up to 10 to 12 months, with about 20 percent of dogs living two or more years after diagnosis. If initial surgery is out of the question due to finances or lack of pet insurance coverage, owner preference or other factors, palliative care should be sought until such time as humane euthanasia becomes appropriate. Radiation therapy can be used at the tumor site to alleviate pain, and several medications can be used to also address pain. These include nonsteroidal anti-inflammatory drugs.
The prognosis for cats with osteosarcoma is better than the prognosis for dogs; often, amputation is curative for cats. However, because 90 percent of dogs will have metastasis to the lungs at the time of presentation for osteosarcoma, the disease is almost always eventually fatal. There is no easy answer when faced with osteosarcoma — your vet will help you arrive at the best decision for your family while ensuring that your pet is comfortable and happy.
Case study: 5-year-old Labradoodle
Treatment: leg amputation, chemotherapy
Max is not the type to balk at a walk, so when mom Kristy noticed him limping, she took it seriously.
“He seemed to be in pain, so I knew I needed to have him checked out.”
Veterinarians discovered a spongy spot in Max’s paw and suspected osteosarcoma, which tests confirmed. Amputation of the entire leg to keep the cancer from spreading and follow-up chemotherapy was the course of treatment, and a full recovery was uncertain. Yet, despite a six-month prognosis, Max is going strong and just celebrated his fifth birthday.
“He’s a happy, three-legged pup who runs and plays just like he did before,” says Kristy. “His current status is healthy — and spoiled.”
Case study: 4-year-old Golden Retriever
Treatment: leg amputation, chemotherapy
When Frodo started limping during a beach romp, his family wasn’t overly concerned.
“We rested him and he seemed to improve,” says mom Tabatha, “but then the limp came back.”
Shortly after, veterinarians discovered a tumor on Frodo’s hind leg, changing the diagnosis from torn ligament to osteosarcoma. An amputation and chemotherapy gave Frodo five cancer-free months before vets found that the cancer had metastasized to his lungs. However, despite his prognosis, Frodo is a warrior.
“He swims, plays with other dogs and has a happy life,” says Tabatha. “We know osteosarcoma will take him eventually, but we are eternally grateful for the time we have with him.”