Soft tissue sarcoma

What is soft tissue sarcoma? 

A soft tissue sarcoma is a cancer of connective tissue in the body. Connective tissue is the building block of the skeleton and includes tissues such as muscle, bone, tendon, ligament, blood vessels, nerves and the fibrous glue that holds all of these together. It includes the legs, body wall, pelvis, rib cage, and the scaffold of the head and neck. 

Sarcomas are classified according to their parent tissue, e.g. osteosarcoma is a tissue of bone, fibrosarcoma is a tumour of fibrous tissue, haemangiosarcoma is a tumour of blood vessel walls, and synovial cell sarcoma is a tumour of synovium, or joint tissue. 

Many sarcomas, especially those growing just under the skin (subcutaneous tumours), are classified by oncologists as one large group, called soft tissue sarcomas, because despite having subtly different parent tissues, they behave in a very similar fashion in terms of growth, spread and response to treatment. 

What does a low grade sarcoma mean?

Sarcomas are typically further classified into grades 1, 2 or 3. This is determined by the appearance of the cancer under the microscope. The pathologist examining the tissue is looking for features such as how rapidly the cells are dividing, how well organised or disorganised they appear in the sample, and whether there is any evidence of cancer cells growing into or occupying tiny blood vessels in the mass, as this can be linked with a higher chance of spread, now or in the future. 

All sarcomas are malignant (have the potential to spread) but the risk increases with the grading. Grade 1 is the least aggressive, with the lowest chance of spread, and possibly a lower chance of regrowth or recurrence following surgery or radiation therapy. Grade 3 is the most malignant with the highest chance of spread and also the most rapidly dividing cells and invasive cells, which can make treating the original tumour (the ‘primary’) more challenging. Grades 1,2 and 3 are also sometimes referred to as low, intermediate and high grade. 

How can I tell if my dog/cat has a sarcoma? 

A sarcoma is first and foremost a mass, growth or swelling. When sarcomas develop beneath the skin they might appear as soft, squishy, fatty appearing lumps and in fact, many are mistaken for benign harmless fatty tumours (lipomas). This is a common cause for the diagnosis of soft tissue sarcoma to be delayed which might impact treatment options and outcome. Sarcomas beneath the skin are typically painless, and the haired skin will often freely move over the top of the mass. The lump may be movable beneath the skin, or it may be stuck down to deeper tissues making it immobile. When sarcomas develop in nerves, bones and joints often they cause the animal pain, and this might manifest as muscle loss, limping, reluctance to exercise or play, and sometimes changes in behaviour due to the mass causing discomfort. If any of these signs are observed in your pet, or if you find any lump or bump, we would recommend a visit to your family veterinary surgeon to get them examined. 

What are the causes of sarcomas? 

Most cancers in pets have no specific cause. We know sunlight can cause skin cancer, and second-hand smoke can increase the risk of some cancers in pets, as can some herbicides. Sarcomas, however, are likely to have a large genetic component which means that if your pet develops a sarcoma it is not because you have, or have not, done something. What you can do however is seek the best advice possible from your family veterinary surgeon about what the diagnosis of sarcoma means. You can also ask to be referred to a specialist veterinary oncology centre for further advice, treatment and support. 

How are sarcomas diagnosed? 

Your family veterinary surgeon will first of all want to examine your pet and the lump. They will likely feel the mass, determine whether it is mobile or fixed, and likely measure the diameter and record it on your pet’s medical record for future reference and comparison. 

The next step is likely to suggest using a needle and syringe (the same sized needle or smaller as the one used to give vaccinations) to suck out a few cells and put them onto a glass slide for the pathologist to examine. It is likely a diagnosis can be made from this single test, but in some cases, a larger core biopsy might need to be taken, or even a thin wedge of tissue. These biopsies are often taken under sedation with local anaesthetic to numb the area, or sometimes under a very light anaesthetic. 

Once your vet has made a diagnosis they will talk to you about ‘staging’ the tumour, i.e. making sure there are no signs of spread within the body. This is normally done with a combination of x-rays, ultrasound, and in some cases a CT scan, which allows the radiologist to look inside body areas including the skull, lungs and abdomen for any early signs of cancer spread. A CT of the tumour itself also allows the family veterinary surgeon, or the specialist cancer surgeon, accurately plan surgery to make sure it is performed successfully. 

It is these two pieces of information, namely WHAT is the tumour, and WHERE is the tumour, that make possible a discussion about what OPTIONS exist, and of course, what might happen if nothing is done. 

How are sarcomas treated? 

Sarcoma treatment depends on the exact origin of the tumour. Treatment options for osteosarcomas, tumours of bone, are covered on the osteosarcoma page on our website. This section will cover exclusively treatment for soft tissue sarcomas. 

In modern veterinary cancer therapy, three main types of treatment are sometimes used; cancer surgery, chemotherapy (anti-cancer drugs), and radiation therapy (powerful x-ray type beams that damage cancer cells). 

Most soft tissue sarcomas are managed by surgery, either exclusively, or in combination with one or two of the other therapies. 

Cancer surgery for soft tissue sarcomas ideally aims to remove the lump that is visible and all the invisible cancer extensions that cannot be seen or felt. CT will sometimes help the surgeon identify how far these extend away from the mass, and how much normal tissue (the ‘margin’) needs to be removed in addition to the mass to achieve a tumour-free wound bed. Some surgical wounds can be closed quite easily, but occasionally with larger tumours, a skin flap, or a skin graft might be needed to help cover the defect. This is another reason why catching a tumour early is so important, as the surgery required to achieve a good outcome may well be smaller. 

 If the tumour cannot be completely removed by surgery alone, or examination of the biopsy specimen showed that some cancer cells had been left behind in the wound, then a referral to an oncologist to discuss options might be a sensible, or direct to a radiation oncology centre. Radiation in pets is very similar to people, except in our animals they need to be under light anaesthesia during treatment so they lie still. The exact number of treatments varies depending on specific circumstances, but anywhere in the range from 4-20 might be needed, with one dose typically being given daily.   

If the pathologist examines the soft tissue sarcoma and diagnoses a high grade, or grade 3 cancer, then a discussion with a specialist oncologist is a good idea. If that is not possible, because cancer therapy is a constantly evolving field, we would recommend your family veterinary surgeon speaking to an oncologist over the phone to learn the latest treatment options available, and whether any clinical trials might be available or open to your pet. Anti-cancer drugs can help tackle tiny spreading clusters of cells in the bloodstream, and so improve the outlook, but again the individual details of each case can vary widely. 

What is the prognosis of sarcomas? 

On the whole, the outlook following treatment for soft tissue sarcomas is better than feared, especially bearing in mind this is a malignant cancer. For average sized grade 1 and 2 soft tissue sarcomas, treated with surgery and possibly radiation therapy, approximately three-quarters of patients will be alive three years later. For the most malignant tumours, the grade 3 tumours, unfortunately, less than half are alive three years after diagnosis. 

The goal of treatment in all cases, however, is to give the patients as happy and comfortable a life as possible, making sure all our decisions are being made for the patient, and not simply to the patient.