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What is osteosarcoma?
Osteosarcoma (also called osteogenic sarcoma) is a type of cancer that starts in the bones. To understand osteosarcoma, it helps to know something about the normal structure and function of bones.
About normal bones
Many people think of bones as just being part of the skeleton, like the steel girders that support a building. But bones actually have a number of different functions.
Some bones help support and protect our vital organs. Examples include the skull bones, breast bone (sternum), and ribs. These types of bones are often referred to as flat bones.
Other bones, such as those in the arms and legs, make a framework for our muscles that helps us move. These are called long bones.
Bones also make new blood cells. This is done in the soft, inner part of some bones called the bone marrow, which contains blood-forming cells. New red blood cells, white blood cells, and platelets are made in bone marrow.
Bones also provide the body with a place to store minerals such as calcium.
Because bones are very hard and don’t change shape − at least once we reach adulthood − we might not think of bones as being alive, but they are complex, living tissues. Like all other tissues of the body, bones have many kinds of living cells. Two main types of cells in our bones help them stay strong and keep their shape.
Osteoblasts help build up bones by forming the bone matrix (the connective tissue and minerals that give bone its strength).
Osteoclasts break down bone matrix to prevent too much of it from building up, and they help bones keep their proper shape.
By depositing or removing minerals from the bones, osteoblasts and osteoclasts also help control the amount of these minerals in the blood.
Osteosarcoma : Osteosarcoma is the most common type of cancer that develops in bone. Like the osteoblasts in normal bone, the cells that form this cancer make bone matrix. But the bone matrix of an osteosarcoma is not as strong as that of normal bones.
Most osteosarcomas occur in children and young adults. Teens are the most commonly affected age group, but osteosarcoma can occur at any age.
In children and young adults, osteosarcoma usually develops in areas where the bone is growing quickly, such as near the ends of the long bones. Most tumors develop in the bones around the knee, either in the distal femur (the lower part of the thigh bone) or the proximal tibia (the upper part of the shinbone). The proximal humerus (the part of the upper arm bone close to the shoulder) is the next most common site. However, osteosarcoma can develop in any bone, including the bones of the pelvis (hips), shoulder, and jaw. This is especially true in older adults.
Subtypes of osteosarcoma : Several subtypes of osteosarcoma can be identified by how they look on x-rays and under the microscope. Some of these subtypes have a better prognosis (outlook) than others.
Based on how they look under the microscope, osteosarcomas can be classified as high grade, intermediate grade, or low grade. The grade of the tumor tells doctors how likely it is that the cancer will grow and spread to other parts of the body.
High-grade osteosarcomas: These are the fastest growing types of osteosarcoma. When seen under a microscope, they do not look like normal bone and have many cells in the process of dividing into new cells. Most osteosarcomas that occur in children and teens are high grade. There are several types of high-grade osteosarcomas.
High-grade surface (juxtacortical high grade)
Other high-grade osteosarcomas include:
Pagetoid: a tumor that develops in someone with Paget disease of the bone
Extra-skeletal: a tumor that starts in a part of the body other than a bone
Post-radiation: a tumor that starts in a bone that had once received radiation therapy
Intermediate-grade osteosarcomas: These uncommon tumors fall in between high-grade and low-grade osteosarcomas. (They are treated as if they are low-grade osteosarcomas.)
Periosteal (juxtacortical intermediate grade)
Low-grade osteosarcomas: These are the slowest growing osteosarcomas. The tumors look more like normal bone and have few dividing cells when seen under a microscope.
Parosteal (juxtacortical low grade)
Intramedullary or intraosseous well differentiated (low-grade central)
The grade of the tumor plays a role in determining its stage and the type of treatment used. For more on staging, see the section, “How is osteosarcoma staged?”
Other types of bone tumors
Several other types of tumors can start in the bones.
Malignant (cancerous) bone tumors
Most other types of bone cancers are usually found in adults and are rare in children. These include chondrosarcoma (cancer that develops from cartilage), malignant fibrous histiocytoma, fibrosarcoma, chordoma, and malignant giant cell tumor of bone. For more information on these cancers.
Many types of cancer that start in other organs of the body can spread to the bones. These are sometimes referred to as metastatic bone cancers, but they are not true bone cancers. For example, prostate cancer that spreads to the bones is still prostate cancer and is treated like prostate cancer. For more information, see the document, Bone Metastasis.
Benign (non-cancerous) bone tumors : Not all bone tumors are malignant. Cells that form benign tumors do not spread to other parts of the body. They are usually not life threatening and can often be cured by surgery. There are many types of benign bone tumors.
Osteomas are benign tumors formed by bone cells.
Chondromas are benign tumors formed by cartilage cells.
Osteochondromas are benign tumors with both bone and cartilage cells.
Other benign bone tumors include eosinophilic granuloma of bone, non-ossifying fibroma, enchondroma, xanthoma, benign giant cell tumor of bone, and lymphangioma.
The rest of this document refers only to osteosarcoma.
What are the risk factors for osteosarcoma?
A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors.
Lifestyle-related risk factors such as body weight, physical activity, diet, and tobacco use play a major role in many adult cancers. But these factors usually take many years to influence cancer risk, and they are not thought to play much of a role in childhood cancers, including childhood osteosarcomas. So far, lifestyle-related factors have not been linked to osteosarcomas in adults, either.
Age : The risk of osteosarcoma is highest for those between the ages of 10 and 30, especially during the teenage growth spurt. This suggests there may be a link between rapid bone growth and risk of tumor formation. The risk goes down in middle age, but rises again in older adults (usually over the age of 60). Osteosarcoma in older adults is often linked to another cause, such as a long-standing bone disease.
Height : Children with osteosarcoma usually are tall for their age. This also suggests that osteosarcoma may be related to rapid bone growth.
Gender : Osteosarcoma is more common in males than in females. Females tend to develop it at a slightly earlier age, possibly because they tend to have their growth spurts earlier.
Race/ethnicity : Osteosarcoma is slightly more common in African Americans than in whites.
Radiation to bones : People who were treated with radiation therapy for another cancer might have a higher risk of later developing osteosarcoma in the area that was treated. Being treated at a younger age and being treated with higher doses of radiation both increase the risk of developing osteosarcoma.
It is not clear if imaging tests that use radiation, such as x-rays, CT scans, and bone scans, raise the risk of developing osteosarcoma. The amount of radiation used for these tests is many times lower than that used for radiation therapy. If there is any increased risk it is likely to be very small, but doctors try to limit the use of these types of tests in children whenever possible, just in case.
Certain bone diseases : People with certain non-cancerous bone diseases have an increased risk of developing osteosarcoma.
Paget disease of the bone: In this condition, abnormal bone tissue forms in one or more bones. It mostly affects people older than 50. The affected bones are heavy and thick but are weaker than normal bones and are more likely to break. Usually this condition by itself is not life-threatening. But bone sarcomas (mostly osteosarcoma) develop in about 1% of people with Paget disease, usually when many bones are affected.
Multiple hereditary osteochondromas: Osteochondromas are benign bone tumors formed by bone and cartilage. Each osteochondroma has a very slight risk of developing into an osteosarcoma. Most osteochondromas can be cured by surgery. However, some people inherit a tendency to develop many osteochondromas, and it may not be possible to remove them all. The more osteochondromas a person has, the greater the risk of developing osteosarcoma.
Inherited cancer syndromes : People with certain rare, inherited cancer syndromes have an increased risk of developing osteosarcoma.
Retinoblastoma is a rare eye cancer of children that can be hereditary. The inherited form of retinoblastoma is caused by a mutation (change) in the RB1 gene. Those with this mutation also have an increased risk of developing bone or soft tissue sarcomas, including osteosarcoma. If radiation therapy is used to treat the retinoblastoma, the risk of osteosarcoma in the bones around the eye is even higher.
The Li-Fraumeni syndrome makes people much more likely to develop several types of cancer, including breast cancer, brain tumors, osteosarcoma, and other types of sarcoma. This syndrome is usually caused by a mutation of the TP53 tumor suppressor gene.
Rothmund-Thompson is another syndrome that includes bone cancer. Children with this syndrome are short and tend to have skeletal problems and rashes. They also are more likely to develop osteosarcoma. This syndrome is caused by abnormal changes in the REQL4 gene.
Other rare inherited conditions, including Bloom syndrome and Werner syndrome, have also been linked to an increased risk of osteosarcoma.
The way in which inherited DNA changes make some people more likely to develop osteosarcoma is explained in the section, “Do we know what causes osteosarcoma?”
Do we know what causes osteosarcoma?
We do not know what causes most osteosarcomas. Scientists have found that osteosarcoma is linked with a number of other conditions, which were described in “What are the risk factors for osteosarcoma?” But in most patients with osteosarcoma, the cause of their cancer is not clear at this time.
Scientists have made a lot of progress in understanding how certain changes in our DNA can cause cells to become cancerous. DNA is the chemical in each of our cells that makes up our genes – the instructions for nearly everything our cells do. We usually look like our parents because they are the source of our DNA. However, DNA affects more than how we look. It influences our risks for developing certain diseases, including some kinds of cancer.
Some genes (parts of our DNA) contain instructions for controlling when our cells grow, divide to make new cells, and die. Genes that help cells grow and divide are called oncogenes. Others that slow down cell division or cause cells to die at the right time are called tumor suppressor genes. Cancers can be caused by DNA changes that turn on oncogenes or turn off tumor suppressor genes.
Some people inherit DNA mutations (changes) that increase their risk of cancer from a parent. In this situation, all of the cells in the body carry the same gene change. These are called germline or inherited mutations. Usually, however, cancer-causing changes are acquired during life rather than inherited before birth. In this case, the change occurs only in the cells that will develop the cancer. These are called somatic or acquired gene changes.
Inherited gene changes : We know the DNA mutations that cause some inherited forms of osteosarcoma. For example:
The Li-Fraumeni syndrome is usually caused by inherited mutations that turn off the TP53 tumor suppressor gene. These mutations give a person a very high risk of developing one or more types of cancer, including breast cancer, brain tumors, osteosarcoma, and other cancers.
Inherited changes in the retinoblastoma (RB1) tumor suppressor gene increase the risk of developing retinoblastoma, a type of eye cancer that affects children. Children with this gene change also have an increased risk for developing osteosarcoma.
Acquired gene changes : Most osteosarcomas are not caused by inherited DNA mutations. They are the result of gene changes acquired during the person’s lifetime. These changes are present only in the cancer cells and are not passed on to children.
Although radiation therapy is very useful in treating some forms of cancer, it can also cause cancer by damaging DNA. This is why people who get radiation therapy to treat another cancer are more likely to later develop osteosarcoma in the treated site.
Other DNA changes have no clear cause but may result from random errors that occur when cells reproduce. Scientists do not know exactly why these changes happen to some people but not to others. Before a cell divides, it must copy its DNA so that both new cells have the same set of instructions. Sometimes mistakes are made during this copying process. Cells that are dividing quickly are more likely to create new cells with mistakes in their DNA, which increases the risk that a cancer such as osteosarcoma may develop. This may be why some normal situations (such as the teenage growth spurt) and diseases (such as Paget disease of bone) that cause rapid bone growth increase the risk of osteosarcoma.
Other than radiation, there are no known lifestyle-related or environmental causes of osteosarcoma, so it is important to remember that there is nothing people with these cancers could have done to prevent them.
Researchers now understand some of the gene changes that occur in osteosarcomas, but it’s not always clear what causes these changes. As we learn more about what causes osteosarcoma, hopefully we will be able to use this knowledge to develop ways to better prevent and treat it.
Can osteosarcoma be prevented?
The risk of many adult cancers can be reduced with certain lifestyle changes (such as maintaining a healthy weight or quitting smoking), but at this time there are no known ways to prevent osteosarcoma.
Most known risk factors for osteosarcoma (age, height, race, gender, and certain bone diseases and inherited conditions) cannot be changed. Other than radiation therapy, there are no known lifestyle-related or environmental causes of osteosarcoma, so at this time there is no way to protect against most of these cancers.
Can osteosarcoma be found early?
At this time, there are no widely recommended screening tests for this cancer. (Screening is testing for cancer in people without any symptoms.)
Still, most osteosarcomas are found at an early stage, before they have clearly spread to other parts of the body. Symptoms such as bone pain or swelling often prompt a visit to a doctor. (For more on possible signs and symptoms of osteosarcoma.
People with certain bone diseases or in families known to carry inherited conditions that raise the risk of this cancer (listed in “What are the risk factors for osteosarcoma?”) should talk with their doctors about the possible need for increased monitoring for this disease. This type of cancer usually does not run in families, but looking out for the early signs of cancer is important if it is to be treated successfully.
How is osteosarcoma diagnosed?
Osteosarcomas are usually found when a person reports signs or symptoms they have noticed to their doctor. If a tumor is suspected, tests will be needed to confirm the diagnosis.
Signs and symptoms of osteosarcoma
Pain and swelling : Pain in the affected bone (usually around the knee or in the upper arm) is the most common symptom of osteosarcoma. At first, the pain might not be constant and may be worse at night. The pain often increases with activity and may result in a limp if the tumor is in a leg.
Swelling in the area is the next most common symptom, although it may not occur until several weeks after the pain starts. Depending on where the tumor is, it may be possible to feel a lump or mass.
Unfortunately, limb pain and/or swelling are very common in normal, active children and teens, and might not prompt a doctor visit right away. This can delay a diagnosis. These symptoms are less common in adults and should be a sign to see a doctor as soon as possible.
Bone fractures (breaks) : Although osteosarcoma might weaken the bone it develops in, the bones often do not break. Telangiectatic osteosarcomas, which are rare, tend to weaken bones more than other forms of osteosarcoma and are more likely to cause a fracture at the tumor site.
People with a fracture next to or through an osteosarcoma often describe a limb that was sore for a few months and suddenly became very painful when the fracture occurred.
Medical history and physical exam : If a person has signs or symptoms that suggest a tumor in or around a bone, the doctor will want to take a complete medical history to find out more about the symptoms. A physical exam can provide information about the tumor and other health problems. For example, the doctor may be able to see or feel an abnormal mass.
The doctor may also look for problems in other parts of the body. When people (especially adults) do have cancer in the bones, it is often the result of cancer that started somewhere else and then spread to the bones. If the doctor suspects a person could have osteosarcoma (or another type of bone tumor), more tests will be done. These might include imaging tests, biopsies, and/or lab tests.
Imaging tests : Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. Imaging tests may be done for a number of reasons, including:
To help find out if a suspicious area might be cancer
To help determine if a cancer may have started in another part of the body
To learn how far cancer may have spread
To help determine if treatment has been effective
To look for signs that the cancer may have come back
Patients who have or may have osteosarcoma will have one or more of these tests.
Bone x-ray : Doctors can often recognize or at least suspect osteosarcoma on plain x-rays of the bone. But other imaging tests may be needed as well.
Even if results of an x-ray strongly suggest a person has osteosarcoma, a biopsy will still be needed to confirm that it is cancer rather than some other problem, such as an infection.
Magnetic resonance imaging (MRI) scan : MRI scans provide detailed images of soft tissues in the body. These scans use radio waves and strong magnets instead of x-rays, so no radiation is involved. The energy from the radio waves is absorbed by the body and then released in a pattern formed by the type of body tissue and by certain diseases. A computer translates the pattern into a very detailed image of parts of the body. A contrast material called gadolinium may be injected into a vein before the scan to better see details.
Often, an MRI scan is done to better define a bone mass seen on an x-ray. MRI scans can usually tell if the mass is likely to be a tumor, an infection, or some type of bone damage from other causes. MRI scans can also help show the exact extent of a tumor, as they provide a detailed view of the marrow inside bones and the soft tissues around the tumor. Sometimes, the MRI can help find small bone tumors several inches away from the main tumor (called skip metastases). Defining the extent of an osteosarcoma is very important when planning surgery. An MRI scan usually gives better details than a CT scan (described below).
Having an MRI scan can take up to an hour. You (or your child) may have to lie on a table that slides inside a narrow tube, which is confining and can be distressing. The newer, more open MRI machines can help with these feelings, but the test still requires staying still for long periods of time. The machines also make buzzing and clicking noises that may be disturbing. Sometimes, younger children are given medicine to help keep them calm or even sleep during the test.
Computed tomography (CT) scan : The CT scan uses x-rays to produce detailed cross-sectional images of parts of the body. Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around a person lying on a table. A computer then combines these pictures into images of slices of the part of the body being studied. Unlike a regular x-ray, a CT scan creates detailed images of the soft tissues in the body.
Before the test, you (or your child) may be asked to drink a contrast solution and/or get an intravenous (IV) injection of a contrast dye that helps better outline abnormal areas in the body. If the contrast dye is to be injected, you (or your child) may need an IV line. The contrast may cause some flushing (a feeling of warmth, especially in the face). Some people are allergic and get hives. Rarely, more serious reactions like trouble breathing or low blood pressure can occur. Be sure to tell the doctor if you (or your child) have any allergies or have ever had a reaction to any contrast material used for x-rays.
A CT scanner has been described as a large donut, with a narrow table in the middle opening. During the test, the table slides in and out of the scanner. You (or your child) will need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken. In some cases, children may need to be sedated before the test to stay still and help make sure the pictures come out well.
CT scans are sometimes used to look at the affected bone to see if the tumor has grown into nearby muscle, fat, or tendons, although MRI is often better for this. A CT scan of the chest is often done to look for spread of the cancer to the lungs.
Chest x-ray : This test is sometimes done to see if cancer has spread to the lungs. It can find larger tumors, but it is not as good as a CT scan for spotting smaller tumors. If a CT scan of the chest is done, a chest x-ray may not be needed.
Bone scan : A bone scan can help show if a cancer has spread to other bones, and is often part of the workup for people with osteosarcoma. This test is useful because it provides a picture of the entire skeleton at once.
For this test, a small amount of low-level radioactive material is injected into a vein (intravenously, or IV). The substance settles in areas of damaged bone throughout the entire skeleton over the course of a couple of hours. You (or your child) then lie on a table for about 30 minutes while a special camera detects the radioactivity and creates a picture of the skeleton. Younger children may be given medicine to help keep them calm or even asleep during the test.
Areas of active bone changes appear as “hot spots” on the skeleton because they attract the radioactivity. Hot spots may suggest areas of cancer, but other bone diseases can also cause the same pattern. To make an accurate diagnosis, other imaging tests such as plain x-rays, MRI scans, or even a bone biopsy might be needed.
Positron emission tomography (PET) scan : For a PET scan, a radioactive substance (usually a type of sugar related to glucose, known as FDG) is injected into the blood. The amount of radioactivity used is very low. Because cancer cells in the body are growing quickly, they absorb large amounts of the radioactive sugar. After about an hour, you (or your child) will lie on a table in the PET scanner for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body. The picture is not finely detailed like a CT or MRI scan, but it provides useful information about the whole body.
PET scans can help show the spread of osteosarcomas to the lungs, other bones, or other parts of the body, and can also help in following the response to treatment.
Some newer machines can do a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET with the more detailed appearance of that area on the CT.
Biopsy : Although the results of imaging tests may strongly suggest that a person has some type of bone cancer, a biopsy (removing some of the tumor for viewing under a microscope and other lab testing) is the only way to be certain. A biopsy is also the best way to tell osteosarcoma from other types of cancer.
If the tumor is in a bone, it is very important that a surgeon experienced in treating bone tumors does the biopsy.Whenever possible, the biopsy and surgical treatment should be planned together, and the same orthopedic surgeon should do both the biopsy and the surgery. Proper planning of the biopsy location and technique can prevent later complications and reduce the amount of surgery needed later on.
There are 2 main types of biopsies.
Needle biopsy : For these biopsies, the doctor uses a hollow needle to remove a small sample of the tumor. The biopsy is usually done with local anesthesia, where numbing medicine is injected into the tissue over the biopsy site. In some cases, sedation or general anesthesia (where the patient is asleep) may be needed.
Often, the doctor can aim the needle by feeling the suspicious area if it is near the surface of the body. If the tumor cannot be felt because it is too deep, the doctor can guide the needle while viewing a CT scan. This is called a CT guided needle biopsy.
Core needle biopsy: In a core needle biopsy, the doctor uses a large, hollow needle to remove a small cylinder of tissue from the tumor.
Fine needle aspiration (FNA) biopsy: For an FNA biopsy, the doctor uses a very thin needle attached to a syringe to withdraw (aspirate) a small amount of fluid and some cells from the tumor. This type of biopsy is rarely used for bone tumors.
Surgical (open) biopsy : In an open biopsy, the surgeon cuts through the skin, exposes the tumor, and then cuts out a piece of it. These biopsies are usually done under general anesthesia (with the patient asleep). They can also be done using a nerve block, which makes a large area numb.
This type of biopsy must be done by an expert in bone tumors. Otherwise it could result in problems later on. For example, if the tumor is on the arm or leg, it’s possible the chance for saving the limb may be lost. If possible, the opening through the skin used in the biopsy should be lengthwise along the arm or leg because this is the way the incision will be made for the operation to remove the cancer. The entire scar of the original biopsy will also have to be removed, so making the biopsy incision this way lessens the amount of tissue that needs to be removed later on.
Testing the biopsy samples : All samples removed by biopsy are sent to a pathologist (a doctor specializing in lab tests) to be looked at under a microscope. Tests looking for chromosome or gene changes in the tumor cells may also be done. These tests may help tell osteosarcoma from other cancers that look like it under the microscope and can sometimes help predict whether the osteosarcoma is likely to respond to therapy.
If osteosarcoma is diagnosed, the pathologist will assign it a grade, which is a measure of how quickly the cancer is likely to grow and spread, based on how it looks under a microscope. Cancers that look somewhat like normal bone tissue are described as low grade, while those that look very abnormal are called high grade.
Blood tests : Blood tests are not needed to diagnose osteosarcoma, but they may be helpful once a diagnosis is made. For example, high levels of certain chemicals in the blood such as alkaline phosphatase and lactate dehydrogenase (LDH) can suggest that the osteosarcoma may be more advanced than it appears.
Other tests such as blood cell counts and blood chemistry tests are done before surgery and other treatments to get a sense of a person’s overall health. These tests are also used to monitor a person’s health while they are getting chemotherapy.
How is osteosarcoma staged?
Staging is the process of finding out how far a cancer has spread. The treatment and prognosis (outlook) for osteosarcoma depend, to a large extent, on the stage of the cancer when it is first diagnosed.
The stage of an osteosarcoma is based on the results of physical exams, imaging tests, and any biopsies that have been done, which were described in the section “How is osteosarcoma diagnosed?”
A staging system is a standard way for the cancer care team to sum up the extent of the cancer. Two formal staging systems, described below, are sometimes used to describe the extent of an osteosarcoma. But doctors often use a simpler system that divides osteosarcomas into 2 groups – localized and metastatic – when deciding on the best course of treatment.
Localized versus metastatic osteosarcoma
Localized osteosarcoma : A localized osteosarcoma is seen only in the bone it started in and possibly the tissues next to the bone, such as muscle, tendon, or fat. About 4 out of 5 osteosarcomas are thought to be localized when they are first found. But even when imaging tests do not show that the cancer has spread to distant areas, most patients are likely to have micrometastases (very small areas of cancer spread that can’t be detected with tests), which is why chemotherapy is an important part of treatment for most osteosarcomas. If it isn’t given, the cancer might be more likely to come back after surgery.
Doctors further divide localized osteosarcomas into 2 groups. Resectable cancers are those in which all of the visible tumor can be removed by surgery. Osteosarcomas that cannot be completely removed by surgery are called non-resectable (or unresectable).
Metastatic osteosarcoma : A metastatic osteosarcoma has clearly spread to other parts of the body such as the lungs or to other bones not directly connected to the bone the tumor started in. Most often it spreads to the lungs, but it can also spread to other bones, the brain, or other organs.
About 1 out of 5 osteosarcoma patients has metastatic spread at the time of diagnosis. These patients are harder to treat, but some can be cured if the metastases can be removed by surgery. The cure rate for these patients improves markedly if chemotherapy is also given.
Musculoskeletal Tumor Society (MSTS) Staging System
One system commonly used to stage osteosarcoma is the MSTS system, also known as the Enneking system. It is based on 3 key pieces of information:
The grade of the tumor (G)
The extent of the main (primary) tumor (T)
If the tumor has metastasized (spread) to nearby lymph nodes (bean-sized collections of immune system cells) or other organs (M)
The grade of a tumor is a measure of how likely it is to grow and spread, based on how it looks under the microscope. Tumors are either low grade (G1) or high grade (G2).
The extent of the primary tumor is classified as either intracompartmental (T1), meaning it has basically remained within the bone, or extracompartmental (T2), meaning it has extended beyond the bone into other nearby structures.
Tumors that have not spread to the lymph nodes or other organs are considered M0, while those that have spread are M1.
These factors are combined to give an overall stage, using Roman numerals from I to III. Stages I and II are further divided into A for intracompartmental tumors or B for extracompartmental tumors.
G1 or G2
Low-grade, localized tumors are stage I.
High-grade, localized tumors are stage II.
Metastatic tumors (regardless of grade) are stage III.
AJCC staging system : Another system sometimes used to stage bone cancers is the American Joint Commission on Cancer (AJCC) system. The AJCC uses one system to describe all bone cancers, including osteosarcomas. The AJCC staging system for bone cancers is based on 4 key pieces of information:
T describes the size of the main (primary) tumor and whether it appears in different areas of the bone.
N describes the extent of spread to nearby (regional) lymph nodes (small bean-shaped collections of immune system cells). Bone tumors rarely spread to the lymph nodes.
M indicates whether the cancer has metastasized (spread) to other organs of the body. (The most common sites of spread are to the lungs or other bones.)
G stands for the grade of the tumor, which is a description of how the cells look under a microscope. Low-grade tumor cells look more like normal cells, and are less likely to grow and spread quickly, while high-grade tumor cells look more abnormal.
Numbers after T, N, M, and G provide more details about each of these factors.
T categories of bone cancer
T0: There is no evidence of a main (primary) tumor.
T1: The tumor is 8 cm (around 3 inches) across or less.
T2: The tumor is larger than 8 cm across.
T3: The tumor has “skipped” to another site or sites within the same bone.
N categories of bone cancer
N0: The cancer has not spread to regional (nearby) lymph nodes.
N1: The cancer has spread to nearby lymph nodes.
M categories of bone cancer
M0: There is no distant metastasis.
M1: Distant metastasis (spread of the cancer to tissues or organs far away from the original bone tumor).
M1a: The cancer has spread only to the lung.
M1b: The cancer has spread to other distant sites in the body.
Grades of bone cancer
Note: The grades used for the AJCC system are different from those in the MSTS system. There are other differences between the systems as well. To avoid confusion, it may help to ask your (child’s) doctor which staging system he or she uses.
G1, G2: Low grade
G3, G4: High grade
Stage grouping : Once the T, N, and M categories and the grade of the bone cancer have been determined, the information is combined into an overall stage. The process of assigning a stage number is called stage grouping. The stages are described in Roman numerals from I to IV (1 to 4), and are sometimes divided further.
Stage IA : T1, N0, M0, G1 or G2: The tumor is 8 cm across or less and is low grade. It has not spread to nearby lymph nodes or to distant parts of the body.
Stage IB : T2-T3, N0, M0, G1 or G2: The tumor is larger than 8 cm across or has “skipped” to other sites in the same bone. It is low grade. It has not spread to nearby lymph nodes or to distant parts of the body.
Stage IIA : T1, N0, M0, G3 or G4: The tumor is 8 cm across or less and is high grade. It has not spread to nearby lymph nodes or to distant parts of the body.
Stage IIB : T2, N0, M0, G3 or G4: The tumor is larger than 8 cm across and is high grade. It has not spread to nearby lymph nodes or to distant parts of the body.
Stage III : T3, N0, M0, G3 or G4: The tumor has “skipped” to other sites in the same bone. It is high grade. It has not spread to nearby lymph nodes or to distant parts of the body.
Stage IVA : Any T, N0, M1a, any G: The tumor has spread only to the lungs. It has not spread to the lymph nodes or to other distant sites. (It can be any size or grade.)
Stage IVB (if either of these applies) : Any T, N1, any M, any G: The tumor has spread to lymph nodes. It can be any size or grade, and might or might not have spread to other distant sites.
Any T, any N, M1b, any G: The tumor has spread to distant sites other than the lung. It can be any size or grade.
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