Soft Tissue Sarcoma in Pets
Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS
Table of Contents
- Overview
- Symptoms
- Diagnosis
- Treatment
- Outlook
Soft tissue sarcomas are common tumours in dogs, and slightly less common in cats. They typically occur in middle aged to older pets. They can affect any dog with no known breed predisposition. Rarely, sarcomas in cats can be related to an adverse reaction to injections such as vaccination.
Soft tissue sarcomas are all considered malignant, but vary in their behaviour. They are classified as low (grade 1), intermediate (grade 2), or high (grade 3). Low grade tumours are generally slow to grow and unlikely to spread, while high grade tumours are more aggressive, with up to 40% of cases having distant spread.
What are the symptoms of soft tissue sarcomas?
Soft tissue sarcomas are sub-cutaneous (sitting under the skin) but can develop ulceration of the skin as they grow. They can occur anywhere on the body, however, the trunk is the most common site, followed by the limbs. Soft tissue sarcomas often start as relatively small, soft lumps, and grow slowly over months or even years. It is not uncommon for them to look or feel like other types of growth, especially fatty lumps, so it is important to test any new masses appearing.
Which tests are used to diagnose soft tissue sarcomas?
The most common method used to diagnose a mass at first presentation is a fine needle aspirate (FNA). This involves taking a sample of cells from the tumour with a needle, and can be performed easily in a consultation. Soft tissue sarcomas do not exfoliate cells easily, so although an FNA can be suggestive, it is also very common for it to be non-diagnostic. Other common types of tumour, such as lipomas (fatty lumps), exfoliate cells easily, so a lack of result on an FNA suggests more investigation is needed.
The most reliable way to diagnose a soft tissue sarcoma is with a solid tissue biopsy. This can be a needle-core biopsy, taken with a special instrument under sedation, or a surgical biopsy. A biopsy provides a definitive answer, and can also tell us what grade the tumour is.
Higher grade soft tissue sarcomas are more likely to metastasise (spread) around the body. This is most commonly to the lungs, so chest x-rays may be recommended prior to removal of the mass. Any enlarged or abnormal lymph nodes may also be sampled to check for spread. These tests are often performed at the same time as a tissue biopsy.
How are soft tissue sarcomas treated?
Surgery is the treatment of choice for soft tissue sarcoma management, and is often curative. When surgically removing a soft tissue sarcoma tumour, it is recommended to remove at least 3cm of tissue around the visible mass in all directions. This is to try and ensure all tumour cells are removed, as soft tissue sarcomas are known for having a false capsule and are often bigger than they appear. After surgery, the excised tissue is sent to the lab to confirm that all cancer cells have been removed, known as clear margins. If clear margins are not achieved, and tumour cells remain, it is likely that the tumour will slowly recur.
Occasionally, removing the tumour with sufficient margins may be challenging due to the location and/or size of the tumour. Reconstructive surgery or referral to a specialist surgeon may be required. For soft tissue sarcomas occurring on the limbs, amputation may be the only way to remove the tumour in its entirety. Pets often recover from limb amputation very quickly, however, your vet can discuss whether this is the right choice for you and your pet.
If tumour cells are left behind after surgery, radiotherapy can be used - this is the application of radiation to cancer cells to kill them. Radiotherapy can have good success rates, but is only available in certain specialist centres due to the complexity of the equipment required. Soft tissue sarcomas are not amenable to chemotherapy.
Some soft tissue sarcomas are extremely challenging to remove in their entirety. For any proposed surgery, we must weigh the impact on the patient with the likelihood of success (in this case, achieving a cure). In some instances, it may be more appropriate to leave the tumour alone. Soft tissue sarcomas generally grow slowly, and are not painful. If they reach a size where they are affecting the ability to walk, or the tumour becomes ulcerated, infected or painful, we must then consider the pet’s quality of life.
What is the outlook for pets with soft tissue sarcoma?
Prognosis for soft tissue sarcomas is generally very good. If surgical resection is possible, this is usually curative. Soft tissue sarcomas that are high grade are more likely to spread, so have a more guarded prognosis. The vast majority of soft tissue sarcomas are slow growing, however, so even those that cannot be removed, or that recur after unsuccessful surgery, can take many years to become problematic.
Disclaimer
Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.
Page last reviewed: 21st June 2024
Next review due: 21st June 2026