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      Date:   27 June, 2011  

Focus: Small animals - dogs, cats, hamsters, guinea pigs & rabbits

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Malignant fibrosarcoma in a young cat
Dr Sing Kong Yuen, BVMS (Glasgow), MRCVS
27 June, 2011 
Be Kind To Pets
Veterinary Education
Project 2010-0129
Sunday June 26, 2011. I was on duty the whole day as Dr Vanessa Lin was on leave. Usually I work from 9.30 am to 11 am on Sundays and Dr Vanessa Lin starts from 11 am to 5 pm.


1. Malignant fibrosarcomas in a 2-year-old cat. The young couple came for a 2nd opinion as the cat came a few months ago for a right eye injury. Now the cat had multiple large firm hard lumps on the right side of the body mainly and the right eye is a white cloudy mass. The first lump appeared above the right shoulder blade. Then another one grew behind it. Today, the right front leg had a chicken egg's lump under the armpit (axillary lymph node metastasis). There were two smaller lumps to the left side of the midline near the left shoulder blade.

The owner had consulted Vet 1 who did the following:
1. Fine needle aspiration sent to the histopathology lab.
2. Surgical biopsy sent to the histopathology lab as the fine needle aspirate was not useful. Malignant fibrosarcoma was diagnosed.
3. Complete blood cell count indicated a high white cell count initially. X-rays were done.

The fibrosarcomas are malignant and grow aggressively to massive sizes. Surgical excision of the axillary lymph node is highly risky as the cat is not in good health (very thin now) and the tumour has spread to the muscles. The tumour will recur after surgery.

Chemotherapy is not well tolerated by the cat. Radiation therapy is not available for cats in Singapore. Therefore, it would be best to let the cat enjoy the expected one month of his life before the tumour ruptures causing infection and pain and requiring euthanasia. Also, the right front paw shows signs of swelling due to venous obstruction. The cat is thin and has difficulty walking on the right front leg.

A malignant fibrosarcoma is a cancerous growth of the fibrous connective tissue. It is one of the most common musculoskeletal cancers found in cats.

There are four possible causes of fibrosarcoma.

1. Older cats with usually a single, irregularly shaped mass found on the trunk, legs & ears.

2. Rare cases said to be vaccine induced sarcoma.

3. A mutant form of FeLV known as 'feline sarcoma virus' (FeSV). Usually happen in younger cats & occurs as multiple tumour masses.

4. Genetics? This has not been confirmed.

This young cat had the first lump appearing to the right of the midline, between the shoulder blades and had been vaccinated. It is possible that he could be suffering from a vaccine induced sarcoma. Could it be due to genetics?  His right eye ball is no longer normal. Could it be the original site of the sarcoma inside the eyeball ? Could he be having FeLV too as this was not tested. It is hard to say.


Cat owners with very small fast-growing lumps on the vaccination site or in any area may need to find a vet that will remove the lump immediately rather than do fine needle aspiration and surgical biopsy as these test takes time.

By fast-growing lumps, I mean that the lump "suddenly appears" or double in size every week.

Although malignant fibrosarcomas do recur in cats after surgery, early radical surgical excision with a wide margin and repeat surgeries when the lumps recur and are small may lead to an extension of more than one year of life.

By small lumps, I mean those that are less than 1 cm in diameter. Surgical plus chemotherapy prolong lives but chemotherapy is not well accepted by the cat. Radiation therapy has side effects too and is not available for cats and dogs in Singapore. Once the fibrosarcoma has spread, surgery is not advised as fibrosarcomas grow very big very fast and do spread elsewhere in the body.

Prognosis, cost and the welfare of the cat are important considerations in the treatment of fibrosarcomas in the cat. In this case, the owner opted for no treatment and asked me how long the cat would live. I expected one month of good quality life before the armpit tumour ruptures and become infected and painful.

In this young cat, early radical excision of the sarcoma and sending the tumour for histopathology would be my approach to the treatment of this case. This approach is to minimise the chances of metastasis (spread of the tumour).

The client would be advised that the fibrosarcoma will recur and repeat surgeries will be needed. There have been a report by a vet of success using this approach but not much details have been given as she only encountered 3 cases in 26 years and was successful in treating 2/3 cases with repeat surgical excisions. 

From my experience, most pet owners in Singapore have a wait-and- see attitude. Only when the tumour is large will they seek veterinary advices. By then, the fibrosarcomas have spread and become inoperable.
  pug 7 months, injuries serious, deep central ulcerative keratitis, leakage aqueous toapayohvets singapore tpvets_logo.jpg (2726 bytes)


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