How Bone Cancer Is Diagnosed

Cancer in the bones is frequently due to spread, or metastasis, from another non-bone cancer—bone metastases from lung cancer or breast cancer, for instance. Taking a sample, or biopsy, of the affected area of bone not only serves to differentiate between primary bone cancer (which starts in the bone) and metastasis from other cancers (secondary bone cancer) but also helps to identify the specific type of bone cancer.

In the diagnosis of bone cancer, the particular bone that is affected—and the location of the tumor within a particular bone—may both be important clues.

Self-Checks/At-Home Testing

At this time, home tests for the diagnosis of bone cancer have not been developed. Additionally, the early signs and symptoms of bone cancer can easily be confused for other much more common conditions such as sports injuries, or they may at first be attributed to muscular aches and pains.

Labs and Tests

Physical Exam

In cases of bone cancer, the physical examination that a doctor performs will be essentially normal except perhaps for the “soft tissue mass” that may be felt at the primary site of the cancer. This might be detectable as a lump, mound, or swelling extending out from the bone.

Blood Work

The laboratory evaluation, or blood work, can be helpful, although it seldom reveals a particular diagnosis. The levels of two biomarkers in particular—alkaline phosphatase and lactate dehydrogenase—are elevated in a large proportion of patients with bone cancer. However, these levels do not correlate very well with how far the disease has spread in the body.

Biopsy

In the case of a bone biopsy, a small piece of the tumor will be removed and examined under a microscope. It’s considered a simple surgery, usually performed under a general anesthetic, and you will be talked through it before and during the procedure.

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Imaging

X-ray

Suspicion for osteosarcoma very often arises from the appearance of the affected bone on imaging.

Osteosarcoma can have differing appearances on imaging: thinned or “eaten away” appearing areas of bone are referred to as a lytic pattern. Alternatively, the bone may appear thickened, as if reinforced by extra cement, and this is referred to as a sclerotic pattern. Bone cancer can also create a mixed (lytic-sclerotic) pattern on imaging.

Doctors learn about a classic radial or “sunburst”' pattern for osteosarcoma, whereby the surrounding tissue takes on a dense appearance of bone in a radiating, spokes-from-the-hub, sunburst pattern; however this finding is not specific to osteosarcoma and not all osteosarcomas will demonstrate such a pattern.

CT and MRI

Surgery is often a component of treatment, and so it becomes important to determine the extent to which the osteosarcoma occupies bone and soft tissue. This is best seen with cross-sectional imaging techniques such as computed tomography (CT) or magnetic resonance imaging (MRI).

MRI is a procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of sections of the body, including the area of tumor formation. Using MRI to define the extent of the tumor has been shown to be an accurate predictor of the actual tumor extent as determined at the time of surgery.

Radionuclide Bone Scan

A variety of radiographic studies are used as part of the diagnostic evaluation of bone cancer to determine the local and distant extent of disease at the time of diagnosis.

A radionuclide bone scan, using a small amount of radioactive technetium 99m injected into a vein, is useful in detecting additional areas of cancer within the same bone (so-called skip lesions) as well as distant bone metastases. This test is useful because it can show the entire skeleton at once.

This type of radionuclide bone scanning is also useful in detecting additional areas of cancer within the same bone (so-called skip lesions) as well as distant bone metastases. This test is useful because it can show the entire skeleton at once. A positron emission tomography (PET) scan can often provide similar information, so a bone scan might not be needed if a PET scan is done.

Positron Emission Tomography (PET) Scan

In a PET scan, a form of radioactive sugar (known as FDG) is injected into the blood. Many times cancer cells in the body are growing quickly and absorb large amounts of the sugar, creating an image showing FDG uptake in the body in areas of cancer involvement. The image is not 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 seeing how well the cancer is responding to treatment.

Often PET and CT scans will be combined at the same time (PET/CT scan) to allow areas of higher radioactivity on the PET scan to be compared with the more detailed appearance of that area on the CT scan.

Differential Diagnosis

The differential diagnosis of bone diseases of this type include the following:

• Infection
• Other tumors:
  Aneurysmal bone cyst
• Ewing sarcoma
• Chondrosarcoma

The range of possibilities may also be influenced by the location of the primary tumor. For instance, the differential diagnoses of a small jaw lesion include various forms of tooth abscess, osteomyelitis (infection) of the jaw bone, and some of the rare benign tumors (such as ossifying fibromas and brown tumors of hyperparathyroidism).

Staging Overview

Part of diagnosing bone cancer involves staging. Staging means checking the size and location of the main tumor, if it has spread, and where it has spread. Staging helps to decide the treatment, and doctors also consider a cancer's stage when discussing survival statistics.

Localized vs. Metastatic

Staging is based on physical exams, imaging tests, and any biopsies that have been performed. Osteosarcoma may be stage I, II, or III with sub-stages. 

One major consideration in staging is whether the cancer is “localized” or “metastatic.” If localized, the osteosarcoma is seen only in the bone it started in and possibly the tissues next to the bone, such as muscle, tendon, or fat.

The possibility of such tiny metastases is one of the reasons chemotherapy is an important part of treatment for most osteosarcomas. That is, the cancer is more likely to come back after surgery if no chemotherapy is given.

Localized osteosarcomas are further categorized into two groups:

• Resectable cancers are those in which all of the visible tumor can be removed by surgery.
• Non-resectable (or unresectable) osteosarcomas can’t be removed completely by surgery.

Grading

Grading may be incorporated into staging and refers to the appearance of the cancer cells under the microscope. Grading gives an idea of how quickly the cancer may develop.

• Low-grade cancer cells are usually slow growing and less likely to spread.
• High-grade tumors are comprised of cancer cells that are likely to grow quickly and are more likely to spread.

Most osteosarcomas are high-grade, but a type known as parosteal osteosarcoma is usually low-grade.

Staging Systems

The most widely used staging system for osteosarcoma categorizes localized malignant bone tumors by both grade and anatomic extent.

Grade

Low and high grade can indicate a stage.

• Low grade = stage I
• High grade = stage II

Local Anatomic Extent

• The compartmental status is determined by whether or not the tumor extends through the cortex, the dense outer surface of the bone that forms a protective layer around the internal cavity
  • Intracompartmental (no extension through cortex) = A
  • Extracompartmental (extension through cortex) = B

In this system, the following are true:

• Low-grade, localized tumors are stage I.
• High-grade, localized tumors are stage II.
• Metastatic tumors (regardless of grade) are stage III.

There are very few high-grade intracompartmental lesions (stage IIA) because most high-grade osteosarcomas break through the bone’s cortex early in their development.

In younger age groups, the vast majority of osteosarcomas are high-grade; thus, virtually all patients are stage IIB or III, depending on the presence or absence of detectable metastatic disease.

If the cancer comes back after initial treatment, this is known as recurrent or relapsed cancer. But some cancer survivors develop a new, unrelated cancer later. This is called a second cancer.