Chondrosarcoma in Dogs

What is chondrosarcoma?

Chondrosarcomas are tumors that arise from cartilage, which is a connective tissue found where bones meet with joints. Cartilage coats the ends of the bones at joints, providing cushioning while decreasing friction. Cartilage is also found in other areas of the body, such as the ears, nose, trachea (windpipe), and ribs.

Chondrosarcoma is the second most common primary bone tumor in the dog, accounting for 5-10% of primary bone tumors in dogs. The most affected site is the nasal cavity, although it has been reported in the ribs, pelvis, long bones of the limbs, and non-skeletal sites.

"Chondrosarcoma is the second most common primary bone tumor in the dog, accounting for 5-10% of primary bone tumors in dogs."

Chondrosarcoma is most seen in middle-aged dogs, with an average age of onset of 6-8 years old, although it can occur in dogs of any age. It also appears to be more common in medium to large breed dogs. Breeds that may be predisposed include golden retrievers, Labrador retrievers, Bernese mountain dogs, and rottweilers, although results have varied between studies and so breed predispositions are not definitively known.

What causes this type of cancer?

The reason why a particular pet may develop this, or any tumor or cancer, is not straightforward. Very few tumors and cancers have a single known cause. Most seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. 

In the case of chondrosarcoma, no specific risk factors or causes have been identified.

What are the clinical signs of chondrosarcoma?

Chondrosarcoma in dogs most commonly affects the flat bones of the body, such as the ribs, skull, nasal cavity, and pelvis (61-91% of cases). Clinical signs may include localized swelling (which may be painful), decreased appetite, pain, and dehydration. 

Additional clinical signs may depend on the location of the tumor. Chondrosarcoma of the skull, for example, may cause bulging of the eyes. Chondrosarcoma of the nasal passages may cause sneezing and nasal discharge. Chondrosarcoma of the pelvis may lead to pain and weakness in the rear legs

A smaller portion of cases of chondrosarcoma in dogs involve the long bones of the legs. In these dogs, the first sign of disease is often limping on the affected leg. Swelling, which may be painful, may also be seen at the site of the chondrosarcoma.

How is this cancer diagnosed?

Initial tests for chondrosarcoma typically involve screening laboratory tests (such as bloodwork and urinalysis), as well as X-rays (radiographs) of the affected area. In most cases, dogs with chondrosarcoma will not have any visible changes on their bloodwork or urinalysis. Radiographs may show a mass that is indistinguishable from other tumors of the bone or soft tissues.

Fine needle aspiration (FNA) or biopsy will be performed. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

In some cases, results from FNA may not be clear and biopsy may be necessary. A biopsy is a surgical excision of a piece of the tumor. Pieces of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology. Histopathology is helpful to make a diagnosis and can also indicate how the tumor is likely to behave.

How does chondrosarcoma typically progress?

Untreated chondrosarcoma will continue to grow, causing problems that are dependent upon the location of the tumor. Additionally, chondrosarcoma may metastasize, or spread to other areas of the body. Fortunately, chondrosarcoma is less likely to metastasize than other bony tumors of dogs (such as osteosarcoma). Metastasis to the lungs can occur late in the course of disease, but this is not a common occurrence.

Staging (searching for potential spread to other locations in the body) is often recommended before beginning treatment, to ensure that the cancer has not spread. Staging may include bloodwork, urinalysis, X-rays of the lungs, and possibly an abdominal ultrasound. If any lymph nodes are enlarged or feel abnormal, further sampling may be pursued to determine if spread is present.

What are the treatments for chondrosarcoma?

The best treatment for chondrosarcoma is surgical removal. Surgery should be performed with wide margins, removing a large amount of suspected healthy tissue. Chondrosarcoma that occurs in a long bone of the leg, for example, is typically treated with the amputation of that leg.

Chondrosarcoma of the pelvis or ribs is also typically treated with surgery, although the margins may be narrower than those that can be achieved with chondrosarcoma that occurs in a leg. In dogs with chondrosarcoma of the ribs, the mean survival time (the average time that patients diagnosed with this disease will live) is typically 1,000 or more days (3-plus years).

Chondrosarcoma of the nasal passages has a more guarded prognosis. At this location, surgical removal is rarely recommended, and radiation therapy is instead used to slow the growth of the mass. With radiation therapy, the mean survival time of nasal chondrosarcoma is approximately 1-2 years.

"The best treatment for chondrosarcoma is surgical removal."

After surgery, the tissues are sent for histopathology (microscopic examination by a pathologist), to predict, as best as possible, the probability of local recurrence or metastasis. If the entire tumor is submitted for examination, the pathologist can assess if the tumor was completely removed or if additional therapies are necessary (i.e., a second surgery, radiation, or chemotherapy).

Currently, chemotherapy does not appear to offer a significant benefit in managing chondrosarcoma, so, it is not recommended for most cases. Radiation therapy may, however, be recommended. Consultation with a veterinary oncologist (cancer specialist) is the best option for discussion of further treatments.

Is there anything else I should know?

Although metastasis (spread) of chondrosarcoma is unlikely, local recurrence after removal is a risk. This is most likely to occur if the mass was not completely excised.

For this reason, your veterinarian may recommend monitoring the affected site for recurrence after surgery. X-rays of the affected area are typically performed every 3-6 months, depending on the specifics of your pet’s case and your veterinarian’s preferences. This allows early detection of any future recurrence, so that it may be addressed quickly.

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