Osteosarcoma

Osteosarcoma is the commonest cancer that begins in bone. The name simply means a sarcoma made of bone-forming cells: the tumour cells produce osteoid, the immature bone matrix that normal bone cells make.

That is where the simplicity ends. Osteosarcoma is not one disease. Tumours carrying the name range from an aggressive cancer in a teenager that needs months of chemotherapy, to a slow-growing tumour on the surface of the thigh bone in a woman in her thirties that is usually cured by surgery alone.

The essentials

If you read nothing else on this page, these are the points that matter most.

1. Most osteosarcoma is treatable. The usual pattern is chemotherapy, then surgery, then more chemotherapy, roughly a year of treatment. In the largest modern study of high-grade osteosarcoma in people aged 40 and under, around seven in ten were alive five years after diagnosis, and the outlook is better again for the low-grade types.
2. The limb can usually be saved. Removing the tumour and rebuilding the bone with an implant is now the standard approach; amputation is occasionally the better operation, but it is no longer the default.
3. Chemotherapy is given even though the tumour is removed. This is the question patients ask most, and there is a clear answer: surgery alone cures very few people, because microscopic cancer cells are usually already elsewhere in the body at diagnosis.
4. The exact type matters enormously. Some osteosarcomas are low grade and are cured by surgery alone, with no chemotherapy at all. That is decided on the tissue, not the scan.
5. The biopsy should be done by the team that will treat you. A biopsy placed in the wrong spot can compromise the operation that follows.

The rest of this page explains each of those. It is background reading: nothing here replaces the plan your own team will make for your tumour.

Where an osteosarcoma starts

The most useful division is anatomical: where in relation to the bone the tumour arises.

Intramedullary: inside the medullary canal, the marrow cavity at the centre of the bone. This is where the great majority arise, and it includes the conventional high-grade osteosarcoma that most people mean by the word.

Juxtacortical, also called surface: on the outer surface of the bone, growing outward from the cortex rather than from within. These are much less common and, as a group, tend to be less aggressive.

Extraskeletal: in the soft tissues, with no connection to bone at all. A tumour that makes bone but is sitting in muscle. This is rare, occurs in older patients, and behaves differently again.

Within each of those groups there are subtypes that differ mainly in grade: how aggressive the cells look under the microscope. Grade, more than anything else, drives whether chemotherapy is part of the treatment.

Intramedullary osteosarcoma

Conventional osteosarcoma: the one most people have

This is the standard form, and the one the treatment protocols were built around. If you have been told you have osteosarcoma without any qualifying word, this is almost certainly what is meant.

It typically arises at the ends of the long bones, particularly around the knee (the lower end of the thigh bone or the upper end of the shin bone), and is commonest in teenagers and young adults. It is high grade, meaning aggressive under the microscope, and it is treated with chemotherapy before and after surgery, as described below.

Pathologists describe it further according to what the tumour cells are producing: bone, cartilage or fibrous tissue. Those distinctions matter to the pathologist and appear on your report, but they do not change the treatment.

Rarer forms inside the bone

A few uncommon variants also arise in the marrow cavity. Telangiectatic osteosarcoma is largely made up of blood-filled spaces and can be mistaken for a harmless bone cyst on a scan, which is why it is specifically looked for. Small cell osteosarcoma has to be distinguished from Ewing sarcoma. Osteosarcoma can also arise in bone already affected by another condition (most often Paget’s disease, or an area treated with radiotherapy years earlier), which tends to happen in older patients.

All of these are high grade, and all are treated in the same way as conventional osteosarcoma.

Low-grade central osteosarcoma: the exception

One tumour inside the marrow cavity behaves quite differently. Low-grade central osteosarcoma is slow-growing and usually cured by surgery alone, without chemotherapy.

Its difficulty is diagnostic rather than therapeutic: it can closely resemble a harmless bone lesion, and in published series a substantial proportion were not correctly identified on the first biopsy. The scan usually raises the alarm correctly even when the tissue looks equivocal, which is one reason these cases are reviewed by specialist bone pathologists.

Getting it right matters, because a low-grade tumour mistaken for something benign may be treated inadequately, and a minority later develop a high-grade component within them.

Juxtacortical (surface) osteosarcoma

Parosteal osteosarcoma

The commonest of the surface tumours and the classic low-grade osteosarcoma. It most often arises from the back of the lower femur, just above the knee, where it forms a dense, heavily ossified mass attached to the outer surface of the bone. It tends to occur in slightly older patients than conventional osteosarcoma, and it grows slowly, often present for a long time before it is investigated.

Treatment is surgical, and chemotherapy is not usually part of the plan. Because the tumour is low grade, the operation is the treatment, and removing it completely, with a clear margin of healthy tissue, is what determines the outcome. In published series almost all patients keep the limb, though these tumours can sit close to the blood vessels behind the knee, which is one reason the surgery is planned carefully in advance.

The outlook is good: in a series of 84 patients, survival was around 95% at five years and 88% at fifteen.

But there is an important catch, and it is the main thing a patient with this diagnosis needs to know. Recurrence can happen very late. In that series the tumour came back locally in about one in five patients, and nearly half of those recurrences appeared more than ten years after treatment. A small number developed a high-grade component years later, at a median of nearly nine years.

The practical consequence: follow-up for parosteal osteosarcoma must continue for many years, well beyond the five years often assumed to be the finish line. Larger tumours, and those that had entered the marrow cavity, were at higher risk of late recurrence.

Periosteal osteosarcoma

Rarer again: periosteal osteosarcomas make up somewhere between 1% and 6% of osteosarcomas, and less than 2% of all bone cancers. They arise on the surface of the shaft of a long bone rather than at its end, are usually cartilage-rich, and sit at intermediate grade, between parosteal and conventional.

That intermediate position is why their management is genuinely unsettled. Surgical removal is agreed; whether chemotherapy should be added is not. The tumour is rare enough that the available studies are too small to settle the question either way, so the decision is made case by case at a specialist unit, on the individual tumour rather than by rule.

High-grade surface osteosarcoma

The least common of the three surface types. Despite growing on the outside of the bone, it is a high-grade tumour and is treated like conventional osteosarcoma: chemotherapy and surgery.

Extraskeletal osteosarcoma

An osteosarcoma arising in soft tissue, without involving bone or periosteum. It is rare, and differs from the bone-based disease in almost every respect: it occurs in substantially older patients, arises anywhere including internal organs, and is far more often metastatic when it is found.

The outlook is worse than for osteosarcoma arising in bone. In a pooled analysis of nearly 1,300 reported patients, five-year survival was around a third overall, rising to about four in ten among those whose disease was confined to one site and could be removed surgically. Treatment centres on surgery, usually with systemic treatment alongside.

Why chemotherapy is given before and after surgery

This is the part patients most often want explained, and it has a clear answer with a clear origin.

The evidence that chemotherapy is needed at all

Before the late 1970s, high-grade osteosarcoma was treated with surgery (usually amputation), and most patients relapsed. The question of whether adding chemotherapy actually helped was settled by a randomised trial published in 1986. Patients who had definitive surgery were randomly assigned either to chemotherapy or to observation.

Two-year relapse-free survival was 17% in the observation group and 66% in the chemotherapy group.

The authors also noted that the 17% figure matched what had been reported before 1970: the disease had not become milder; treatment had improved. That trial is the reason chemotherapy is standard for high-grade osteosarcoma today.

The reason surgery alone fails is that in most patients the disease is already elsewhere at diagnosis, as microscopic deposits too small for any scan to detect. An operation deals with the tumour you can see. Chemotherapy is aimed at the disease you cannot.

Why some of it is given first

Giving chemotherapy before the operation (neoadjuvant) does three things:

1. It starts treating microscopic spread immediately, rather than after surgery and a recovery period.
2. It often shrinks the tumour and sharpens its boundary, which can make limb-preserving surgery more feasible.
3. It produces a measurement. When the tumour is removed, the pathologist examines it and reports how much viable tumour remains. Less than 10% viable tumour is a good response; 10% or more is a poor response.

That measurement is one of the strongest guides to prognosis available: patients whose tumour responded poorly have roughly twice the risk of a subsequent problem.

Chemotherapy given after the operation is adjuvant, and completes the course.

One thing worth knowing about that measurement

It is natural to assume that a poor response means the drugs should be changed. Large randomised trials have tested exactly that (both adding extra drugs for poor responders and adding extra treatment for good responders), and neither improved survival, while the intensified treatment caused considerably more side effects.

So the response tells your team a great deal about what to expect, and rather less about what to do differently. It guides how closely you are watched rather than which drugs you receive. Improving on that is one of the genuinely unsolved problems in this field, and it is why patients with osteosarcoma are often offered a place in a clinical trial.

Which osteosarcomas do not need chemotherapy

Bringing it together:

This table is a summary of the general pattern, not a treatment plan. Grade is assigned on the actual tissue, and an individual tumour can behave unlike its category: a parosteal osteosarcoma with a dedifferentiated component, for instance, is no longer a low-grade problem.

The operation

Surgery is where the tumour is actually removed, and for every type on this page it follows the same principle set out in surgery for sarcoma: take out the whole tumour together with a cuff of healthy tissue around it, so that no cancer is left behind at the edge.

What differs between patients is how much bone has to go, and what replaces it.

Saving the limb

Limb salvage is now the standard approach, and most patients keep the affected arm or leg. For a conventional osteosarcoma at the lower end of the thigh bone (the commonest site), this usually means removing that segment of bone along with the knee joint, and rebuilding it with a metal implant called an endoprosthesis. These are larger and more complex than a standard joint replacement, and they are one of the main reasons this surgery is done at a specialist centre.

Other reconstructions are used depending on the site: a length of bone in the middle of a limb can sometimes be replaced without disturbing the neighbouring joints, and for a low-grade surface tumour that has not entered the marrow cavity it may be possible to remove only the involved part of the outer bone and leave the rest intact.

Amputation is still occasionally the better operation, usually when the tumour involves the major nerves and blood vessels so extensively that a reconstructed limb would be neither functional nor safe. That is a judgement about what the tumour involves, not about how large it is, and it is discussed openly and well in advance where it is a possibility.

What to expect around the operation

Surgery is timed within the chemotherapy course, usually after the first block of treatment. It is major surgery, and a hospital stay of one to two weeks is usual, followed by a structured rehabilitation programme. Regaining strength and movement around a reconstruction takes months rather than weeks, and physiotherapy is part of the treatment rather than an optional extra.

Implants used to rebuild a limb are mechanical, and over a lifetime they can loosen or wear, so further surgery years later is a realistic possibility. In children who are still growing, reconstruction has to allow for that growth, which brings its own planned sequence of procedures. Both are discussed before the first operation.

Getting the diagnosis right first

Everything on this page depends on knowing precisely which tumour is present, and that is decided on tissue, not on imaging.

This is the reason Australian guidelines advise that a suspected bone or soft tissue tumour be referred to a specialist sarcoma unit before a biopsy is taken, so that the biopsy is planned by the team that will go on to treat it. A biopsy placed badly can compromise the operation that follows. The low-grade central osteosarcoma figures above make the related point about technique: on the tumours that are hardest to call, how the tissue is obtained changes whether the right answer comes back.

The steps involved are set out in tests and diagnosis, and how a plan is agreed in how treatment is planned.

What this means for you

• If you have conventional osteosarcoma, expect a plan of chemotherapy, then surgery, then more chemotherapy, over roughly a year. It is demanding treatment, and it is the treatment that works.
• Expect to keep the limb. Limb salvage with a reconstruction is the usual approach. Where amputation is genuinely the better option, that will be explained fully and in advance.
• If your tumour is one of the low-grade types (parosteal, or low-grade central), surgery alone is likely to be the whole treatment, and chemotherapy is not needed.
• If you have a low-grade tumour, expect long follow-up. Recurrence more than ten years later is well documented, and follow-up is planned around that rather than stopping at five years.
• Ask which type you have, and whether it is high or low grade. Those two answers determine everything else on this page.

If you have been told you may have a bone tumour, or you are a referrer with a patient you are concerned about, the practical thing is early contact with a unit that manages these regularly, ideally before a biopsy is taken.