What is a Soft Tissue Sarcoma?
A soft tissue sarcoma is a malignant cancer that arises from body tissues such as blood vessels, muscle, connective tissue and fatty tissue, among a range of other tissues. Soft tissue sarcomas are quite common in dogs and cats, making up 15% of skin and soft tissue cancers in the dog, and 7% in the cat.
What Should I Know About Soft Tissue Sarcomas
Soft tissue sarcomas have a wide variation in appearance – which seems obvious when you consider these cancers can originate from a variety of different tissues. A feature that is common to many soft tissue sarcomas is that they appear to be well-defined – almost seeming to be contained in a discrete capsule. This can create the impression that the mass might be benign – or safe. However, this is NOT THE CASE! Soft tissue sarcomas, despite feeling benign to palpate are often very malignant, and they should be taken very seriously. Soft tissue sarcomas are not only not benign; they invade into surrounding body tissues very aggressively, meaning that surgery to remove the mass must be aggressive in order to achieve local cure of the cancer.
How is Soft Tissue Sarcoma Diagnosed?
The best way to diagnose soft tissue sarcoma is to biopsy the mass. Biopsy of the mass not only allows the mass to be diagnosed, it also permits grading of the tumour. Grading of tumours is essentially a system of grouping cancers into mild, moderate or severe malignancy, based on their appearance to a pathologist. Grading is important in that it allows your vet to determine the course of treatment for the tumour that will offer the best prognosis for longevity and good quality of life.
|Soft Tissue Sarcoma Grade||Metastatic Rate (Rate of spread to other tissues)|
|Grade 1||<10% metastasise|
|Grade 2||20% metastasise|
|Grade 3||50% metastasise|
How is Soft Tissue Sarcoma Treated?
Surgery is the mainstay of treatment for soft tissue sarcoma. For tumours that have spread beyond the primary lump, chemotherapy may be used to help control secondary tumour growth, although it is not as successful as it is in some other types of cancer.
Surgical removal of a soft tissue sarcoma should be planned carefully, because the tumours invade tissues around the tumour readily. A cancer that is “shelled out” is highly likely to recur. It is therefore recommended to remove soft tissue sarcomas with a margin of normal tissue around the tumour of about 3 cm, and a layer of fascia deep to the cancer – making surgery for removal of even a small mass an important surgery. In cancers that are difficult to remove with such large margins – for example, cancers on the feet or lower limbs – radiation therapy can be used as an adjunctive (supportive) therapy along with surgery to remove the bulk of the cancer.
What is the Prognosis for Soft Tissue Sarcoma?
The prognosis for soft tissue sarcoma is actually quite good – especially if the cancer can be completely removed at the first surgical attempt. However, there are some key factors that worsen prognosis, and these are…
- Large tumour size – large tumours are inherently more difficult to remove completely. Careful planning for surgery of large tumours is required, and your vet may consult a surgical oncologist for assistance in planning surgery of large cancers
- Incomplete surgical resection – incomplete removal of a cancer leads to cancer cells remaining in your dog or cat. This leads to cancer recurrence and a worse prognosis
- High cancer grade – Grade 3 soft tissue sarcomas have a 46-50% rate of cancer spread to other organs – most commonly the lungs – worsening the prognosis
Overall, the median survival time for dogs with soft tissue sarcomas is 1400 days, with about 33% of dogs eventually dying from tumour-related causes. Dogs with malignant or high grade soft tissue sarcomas, however, have a median survival time of between 236 and 532 days (8-18 months)
If you have any questions about a lump on your dog, please contact your veterinarian immediately for advice. Remember, the earlier you have a lump examined and assessed, the earlier – and hence more successful – treatment can be started!