Pleomorphic Osteosarcoma in Cats​

Pleomorphic osteosarcoma is a rare but aggressive form of cancer that affects the bones of cats. It is a subtype of osteosarcoma, a malignant tumor primarily composed of bone-forming cells. 

Osteosarcoma in cats can be categorized into two main types:

conventional osteosarcoma and pleomorphic osteosarcoma.

Conventional osteosarcoma, the more common type, features uniform bone-forming cells and primarily affects the limbs. Pleomorphic osteosarcoma, rarer in cats, is characterized by irregular, varied-shaped cells and is more aggressive. It often appears in the limbs, but can also affect the spine, ribs, or jaw. Both types share a tendency to metastasize, particularly to the lungs, making early diagnosis and treatment crucial.

What is Pleomorphic Osteosarcoma in Cats?

Pleomorphic osteosarcoma is a type of cancer that develops in the bones, particularly in the long bones of cats. The term "pleomorphic" refers to the variation in cell shape and size found in the tumor, making it more difficult to treat and diagnose compared to other, more uniform types of osteosarcoma. Osteosarcoma is a highly malignant cancer, meaning that it has a tendency to spread rapidly to other parts of the body, especially the lungs. While osteosarcoma is relatively rare in cats, pleomorphic osteosarcoma is even more so.

Osteosarcomas originate in the bone cells, and in cats, they most commonly affect the limbs, though they can also appear in the ribs, skull, and spine. In some cases, these tumors may develop in the jawbone. Pleomorphic osteosarcoma is distinguished by the abnormal, polymorphic (variable) appearance of the tumor cells, which often leads to difficulties in diagnosis.

Symptoms of Pleomorphic Osteosarcoma in Cats

The symptoms of pleomorphic osteosarcoma in cats depend on the location and size of the tumor. In most cases, cats will exhibit pain and swelling in the affected limb or body part. The following are common symptoms associated with this type of cancer:

• Limping or Lameness: This is the most common sign of bone cancer in cats. If the tumor is in the limbs, the cat may refuse to put weight on the affected leg or show signs of pain when walking.
• Swelling or Lumps: A visible lump or swelling may appear over the tumor site, though it is not always immediately noticeable.
• Pain and Discomfort: Cats with pleomorphic osteosarcoma often show signs of pain, which may include changes in behavior, reduced activity, and difficulty getting up or lying down.
• Loss of Appetite: As with many cancers, cats with osteosarcoma may lose interest in food and show a general lack of appetite.
• Weight Loss: Associated with the loss of appetite and the spread of the cancer, weight loss is often observed.
• Respiratory Issues: If the cancer has metastasized to the lungs, cats may develop breathing problems, coughing, or labored breathing.
• Difficulty Moving or Stretching: In cases where the tumor is in the spine or jaw, the cat may have difficulty moving its neck, back, or mouth.

Causes and Risk Factors

While the exact cause of pleomorphic osteosarcoma in cats is not fully understood, several factors may increase the likelihood of its development:

1. Age: Older cats are more likely to develop osteosarcoma, although it can occur in younger cats as well. Most cases occur in cats over 8 years old.
2. Breed: Certain breeds may be at higher risk, though osteosarcoma is less common in cats than in dogs. Larger cat breeds may have a slightly higher incidence of bone tumors.
3. Trauma or Injury: Previous trauma to a bone can sometimes contribute to the development of a tumor. While trauma doesn't directly cause cancer, it can create conditions that promote tumor growth.
4. Genetic Factors: There may be an inherited predisposition to osteosarcoma in certain families of cats, though this has not been as extensively studied as in dogs.

Diagnosing Pleomorphic Osteosarcoma in Cats

The diagnosis of pleomorphic osteosarcoma involves a combination of physical examinations, imaging studies, and tissue biopsies. Early diagnosis is crucial to managing the disease and improving the cat's prognosis.

1. Physical Examination: A veterinarian will start by conducting a thorough physical exam to check for signs of pain, swelling, or abnormal lumps. The cat's medical history, including any trauma or injury to the affected area, will also be considered.
2. Radiographs (X-rays): X-rays are essential for evaluating the size, shape, and location of the tumor. They help determine the extent of bone involvement and whether there is any visible spreading to surrounding tissues.
   
3. CT or MRI Scans: These imaging modalities provide more detailed images and can help assess the tumor's internal structure. A CT or MRI scan can reveal the extent of the tumor, including any metastasis to other parts of the body.
4. Biopsy: A biopsy is necessary to confirm the diagnosis of pleomorphic osteosarcoma. During the biopsy, a small sample of the tumor is removed and examined under a microscope. This allows the veterinarian to observe the pleomorphic characteristics of the cancer cells.
5. Blood Tests: Blood tests are used to check for signs of infection, anemia, or other abnormalities that could indicate metastasis or other complications associated with cancer.

Treatment Options for Pleomorphic Osteosarcoma in Cats

The treatment of pleomorphic osteosarcoma in cats is challenging due to the aggressive nature of the cancer. However, various treatment options may help manage the disease, alleviate pain, and improve the cat's quality of life.

1. Surgery: The primary treatment for osteosarcoma is surgical removal of the tumor. If the tumor is localized and has not spread to other parts of the body, surgery may provide the best chance for long-term survival. In some cases, the affected limb may need to be amputated to remove the tumor completely. Amputation can be a viable option for cats, especially if the tumor is in a limb and has not metastasized.

2. Chemotherapy: Chemotherapy is often used in conjunction with surgery to target any remaining cancer cells. Osteosarcoma has a high potential for metastasis, especially to the lungs, and chemotherapy can help reduce the chances of recurrence or spread. While chemotherapy in cats can be effective, it often comes with side effects like nausea, lethargy, and decreased appetite.

3. Radiation Therapy: Radiation therapy may be used to shrink tumors or treat areas that cannot be surgically removed. It is not as commonly used for osteosarcoma but may be helpful in cases where the tumor is in a location that makes surgery difficult or impossible.

4. Pain Management: Since osteosarcoma is extremely painful, pain management is a critical component of treatment. Cats with osteosarcoma often require pain medications such as NSAIDs, opioids, or gabapentin to control their discomfort. In addition, physical therapy may be recommended to help the cat maintain mobility and strength.

5. Palliative Care: In cases where the tumor is too advanced or metastasis has occurred, palliative care may be the best option. This involves managing symptoms, providing pain relief, and ensuring the cat remains comfortable during the end stages of life.

Prognosis for Cats with Pleomorphic Osteosarcoma

The prognosis for cats with pleomorphic osteosarcoma varies depending on several factors, including the size of the tumor, whether it has metastasized, and the cat's overall health. Generally, the prognosis for osteosarcoma is poor due to its aggressive nature. On average, cats with osteosarcoma live for about 6 to 12 months after diagnosis, though this can vary.

• Without Treatment: If left untreated, pleomorphic osteosarcoma can lead to severe pain, loss of mobility, and metastasis to the lungs, leading to death within a few months.
• With Surgery and Chemotherapy: Cats that undergo surgery and chemotherapy may have a slightly better prognosis, with survival times extending to 1 to 2 years in some cases. However, the risk of recurrence remains high.

Prevention of Pleomorphic Osteosarcoma

Since the exact cause of pleomorphic osteosarcoma is not fully understood, there is no known way to prevent it. However, regular veterinary checkups can help detect early signs of bone tumors, which may improve the chances of successful treatment. Prompt diagnosis and intervention are crucial for managing osteosarcoma effectively.

Conclusion

Pleomorphic osteosarcoma in cats is a rare but serious form of bone cancer. While the prognosis can be challenging, early detection and treatment options such as surgery, chemotherapy, and pain management can help improve the cat’s quality of life. As always, consulting with a veterinary oncologist is the best course of action if a cat is diagnosed with osteosarcoma to explore all potential treatment strategies and make informed decisions based on the individual cat's condition.