Chondrosarcoma in Cats

What is chondrosarcoma?

Chondrosarcomas 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), ribs, and larynx (voice box).

Chondrosarcoma is a rare tumor in cats, but it can occur. This tumor is most common in middle-aged domestic shorthair cats.

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 cause have been identified.

What are the clinical signs of chondrosarcoma?

The clinical signs of chondrosarcoma may vary significantly, depending upon where the tumor arises.

Approximately 44% of cases of chondrosarcoma in cats are found in the long bones, which are the bones that are found in the legs. Cats with chondrosarcoma of the long bones often develop lameness as the first clinical sign of chondrosarcoma. This lameness may be intermittent at first, but often gradually progresses to a consistent lameness that may vary from mild to completely non-weightbearing. Additionally, swelling may be noted at the site of the mass. This swelling may be painful when palpated (touched).

Nearly 26% of chondrosarcoma cases in cats involve the flat bones. The flat bones include the bones of the skull, as well as the ribs, sternum, pelvis, and scapula (shoulder blade). Clinical signs associated with chondrosarcoma at these sites will vary depending on the location of the tumor. You may notice a visible swelling or localized pain, depending on the tumor location. In some cases, decreased appetite or weight loss may be the only sign of chondrosarcoma.

The remaining 30% of chondrosarcoma cases in cats arise as subcutaneous (under the skin) masses. These masses may be noticeable when petting your cat, as a lump or bump.

How is this cancer diagnosed?

Initial screening tests for chondrosarcoma typically involves screening laboratory tests (bloodwork and urinalysis), as well as radiographs (X-rays) of the affected bone or joint. In most cases, cats 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.

If a tumor is suspected, 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 entirely 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 not only helpful to make a diagnosis but can indicate how the tumor is likely to behave.

How does chondrosarcoma typically progress?

Although the mass may grow rapidly, less than 20% of chondrosarcoma cases in cats metastasize (spread) to other parts of the body. Therefore, surgical removal is curative in many cases.

Staging (searching for potential spread to other locations in the body) is recommended prior to surgery, in order 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?

Surgical excision is the treatment of choice for chondrosarcoma, if feasible. This mass is typically removed with wide margins, meaning that healthy tissues surrounding the mass are also removed to reduce the likelihood of recurrence or metastasis (spread to other areas). In chondrosarcoma that involves a limb, this often means amputating the affected limb.

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

Is there anything else I should know?

Although metastasis 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. Radiographs 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.