Soft tissue sarcoma

Soft tissue sarcoma is a rare malignant tumour that grows out of muscle, fat, blood vessels, tendons, ligaments or the sheaths around nerves. For every one of these tumours there are hundreds of completely harmless lumps, so there is no reason to panic about every swelling. But sarcoma has one feature that makes this page worth reading: for a long time it does not hurt and does not get in the way. It grows quietly, and people settle into the idea that it is "just a fatty lump". That is why they come to the doctor late. Below is the simple rule that turns a lump into something worth checking, and the point that is rarely made plainly: this kind of tumour must not be removed in just any operating theatre.

Where it comes from and who gets it

Soft tissue is everything between the skin and the bones: muscle, fat, blood vessels, nerves, tendons, ligaments and the linings of joints. A sarcoma can start in any of them, which is why it turns up anywhere. Most often in the thigh, lower leg or upper arm; less often in the abdomen and the space behind it, where a tumour has room to grow and stays out of the way for a long time.

There are dozens of subtypes and they behave very differently: some grow for years and almost never spread, others are aggressive from the outset. So "sarcoma" is not a complete diagnosis but the name of a group. The exact type is worked out from a piece of tissue under the microscope, and everything that follows depends on it.

In most cases the cause is never established. What is known is that the chance is higher:

• with age — most cases occur in the second half of life, although young adults and children are affected too;
• if that part of the body was treated with radiotherapy in the past: the tumour can appear many years later;
• with certain inherited conditions, such as neurofibromatosis type 1, Li-Fraumeni syndrome or hereditary retinoblastoma;
• where a limb has been swollen for a long time, for example after lymph nodes were removed;
• with untreated HIV infection, which is linked to a separate type, Kaposi's sarcoma, that looks different and is treated differently.

None of these means a sarcoma will happen, and most people who develop one have none of them. An injury does not cause the tumour; what it often does is make someone notice something that was already there.

What the worrying kind of lump looks like

Usually the first and only sign is a lump. No ulcer, no redness, no fever: just a firm mass under the skin.

• it feels solid and is usually painless;
• it sits deep — you feel it with your fingers before you see it;
• it does not slide easily over the surrounding tissue;
• it grows, slowly, over weeks and months, and it does not disappear or shrink;
• pain comes later, once the tumour starts pressing on a nerve or a vessel.

If the tumour has grown inside the abdomen or behind it, there is nothing to feel, and the signs are different and vague: a sense of fullness and heaviness, constipation, swelling of one leg, less often blood in the stools. A tumour near the lung can cause a cough that does not clear or breathlessness.

When to see a doctor without waiting

Here is the rule worth keeping. Have the lump looked at without waiting if even one of these is true:

• it is bigger than a few centimetres — roughly the size of a walnut or larger;
• it is growing, however small it was to begin with;
• it lies deep, within the muscle and beneath the fascia, rather than in the skin itself;
• it hurts;
• a lump has come back in the same place where a supposed fatty lump was once removed.

Any one of these is enough to justify an ultrasound scan and, if the picture is unclear, an MRI scan. And the key point: a lump like this is not watched for months. "Come back in six months and we'll have another look" is not the right answer here. If it does turn out to be a sarcoma, in six months it will be bigger and the operation will be a different one. Asking for a scan and coming back with the question is entirely reasonable; no doctor takes offence at it.

It is probably a lipoma, but you cannot tell by looking

The good news first. The vast majority of soft lumps are benign, and the commonest by far is a lipoma, a collection of ordinary fat. A lipoma is soft, moves under the fingers, grows over years or not at all, sits just beneath the skin and is no threat. There are also cysts, fibromas, enlarged lymph nodes and old bruises after a knock.

But here is what matters and what is seldom said outright: a lipoma and a sarcoma cannot be told apart by appearance or by touch, not by you and not by an experienced doctor. Some sarcomas are made of fatty tissue and feel exactly the same under the fingers. What separates them is imaging and, where needed, a biopsy. So "it looks like a fatty lump" is a guess, not a conclusion, and where any of the features above is present it has to be confirmed with a scan.

Why this tumour must not be removed in passing

This is the most underrated part of the subject. The lump looks straightforward, and it is often taken out in an ordinary theatre as though it were a lipoma: quickly, through a small incision, "while you're here". If a sarcoma turns up under the scalpel, the situation gets worse at once and for a long time.

It comes down to margins. A sarcoma is not removed along its edge but together with a layer of healthy tissue around it, so that not a single cell is left behind. In a routine removal the tumour is shelled out along its capsule, cells are scattered through the wound and along the incision, and a second, far wider operation is then needed, taking out the scar and the whole track the surgeon used the first time. After that the disease comes back in the same place more often, and saving the limb and its function becomes harder.

Two practical conclusions follow:

• a suspicious lump is investigated first and decided about afterwards, never the other way round;
• if the imaging is unclear or suggests a sarcoma, both the biopsy and the surgery are done at a specialist centre that deals with sarcomas routinely.

The biopsy is planned there as well, and not as a formality: the needle is passed along a track that will later be removed in one piece with the tumour. A biopsy done wherever happens to be convenient can close off the chance of keeping an arm or a leg. If you are offered removal of a lump with no imaging at all, ask what exactly is going to be taken out and what an MRI scan would show. That is a fair question, not a lack of trust.

How it is investigated

The usual order is:

• an ultrasound scan — the starting point, quick and often enough to settle the question;
• an MRI scan — the main test for limbs and the trunk, showing size, depth and the relationship to vessels and nerves;
• a CT scan — for tumours in the abdomen and behind it, and to check the lungs, where sarcomas spread most often;
• a core needle biopsy — a cylinder of tissue is taken, and from it the type of tumour and how aggressive it is are established;
• sometimes molecular testing of the sample, because some sarcomas are recognised by a characteristic genetic change.

The pathologist's report does not come back in a day or two; part of the testing is done in specialist laboratories. The wait is wearing, but the whole plan depends on how accurate that answer is, and rushing it is a false economy.

How it is treated

The plan is not made by one doctor but by a team: surgeon, oncologist, radiation oncologist, pathologist and radiologist. Surgery is the backbone, and its aim is to remove the tumour together with a margin of healthy tissue. In the limbs it is usually possible to keep the arm or leg; amputation is now uncommon and is discussed only when there is no other way to preserve function.

What is added to surgery:

• radiotherapy, before the operation to shrink the tumour and make removal easier, or afterwards to reduce the risk of it returning in the same place;
• drug treatment: chemotherapy for the types that respond to it, and targeted medicines for particular kinds of sarcoma; for most types neither is used;
• lung surgery if secondary deposits do appear there and are few in number: they are sometimes removed, and this makes a real difference to the outlook.

After treatment there is follow-up for several years, with examinations and scans, because a recurrence is easier to treat while it is small. If the tumour has spread and cannot be cured, treatment still continues: it holds back the growth and eases symptoms, and alongside it the team that deals with pain and day-to-day wellbeing gets involved. Asking for help with pain is not giving up; it is part of the treatment.

Online consultation

A remote appointment is a good way to settle the main question of the first few days: whether this lump is worth worrying about and how quickly to act. The doctor will ask when it appeared, whether it has changed in size, whether it hurts and how deep it feels, and will advise which test to start with and what the request should say. It is also a convenient way to go through an ultrasound or MRI report you already have, understand what it means, and consider whether to look for a specialist centre before the operation rather than after it. A lump cannot be felt through a screen, so the consultation does not replace a face-to-face examination, but it does stop you losing several weeks to hesitation.

This material is for information only and does not replace medical advice.