TNM Staging of Bone Tumors
“T” stands for “Tumor Size”, “N” for “Lymph Nodes”, and “M” for “Metastasis”. Numbers and/or letters after T (1, 2, and 3), N (0 and 1), and M (0 and 1) provide more details about each of these factors.
Additionally, based on the appearance under the microscope (level of differentiation), cancer cells are assigned a grade (represented by letter ‘G’) from 1 to 3, where 1 indicates most cancer cells look like normal cells (well-differentiated cancer cells) and 3 indicates very few cancer cells look like normal cells (poorly-differentiated cancer cells).
Once T, N, and M categories and grade of cancer cells are determined, this information is combined to assign an overall stage (from I to IV).
T1a N0 M0 G1
The tumor in the bone measures </=8 cm in largest dimension. Tumor is well differentiated. No spread of disease to nearby lymph nodes or distant body parts.
T2-3 N0 M0 G1
The tumor in the bone measures >8 cm in largest dimension or multiple tumors are present in the same bone. Tumor is well differentiated. No spread of disease to nearby lymph nodes or distant body parts.
T1 N0 M0 G2‑3
The tumor in the bone measures </=8 cm in largest dimension. Tumor is moderately to poorly differentiated. No spread of disease to nearby lymph nodes or distant body parts.
T2 N0 M0 G2‑3
The tumor in the bone measures >8 cm in largest dimension. Tumor is moderately to poorly differentiated. No spread of disease to nearby lymph nodes or distant body parts.
T3 N0 M0 G2‑3
Multiple tumors are present in same bone. Tumor is moderately to poorly differentiated. No spread of disease to nearby lymph nodes or distant body parts.
Any T N0 M1a Any G
Cancer has spread to lungs, irrespective of its size and grade. No spread to regional lymph nodes
Any T N1 Any M Any G
Cancer has spread to nearby lymph nodes, irrespective of its size, grade and spread to distant sites. OR Any T Any N M1b Any G Cancer has spread to distant sites.
Bone Tumor Staging Investigations
This is usually the first test which is employed when a bone tumor (or any other bone abnormality) is suspected. In this test, X-rays (high energy radiations emitted by certain elements and x-ray generators) are directed towards the body part to be examined.
These X-rays are reflected back or absorbed by different body tissues depending upon their density. The reflected X-rays are collected on an X-ray sensitive film to produce an image of the bones that reflect most of the x-rays. This test can provide information about the cancerous changes within the bones tissue which appear irregular compared to the nearby bone on X-ray film. Any abnormality observed during this test warrant detailed investigations.
Magnetic resonance imaging (MRI) scan
MRI is very helpful investigation to outline the bone tumor. It is more sensitive to assess the soft tissue and neurovascular involvement by bone tumor. This technique provides detailed images of tissues inside the body using radio waves, strong magnetic field, and gadolinium contrast. It can accurately diagnose the extent of invasion and spread of disease to nearby/distant body parts.
Radionuclide Bone Scan
In this test, a radioactive material, for example, technetium diphosphonate is first injected into the vein of the patient. The radioactive substance gets accumulated in the areas of bones affected by cancer and such areas are then detected with the help of radioactivity detectors.
Positron emission tomography (PET) scan
This technique uses a radioactive substance (e.g.fluorodeoxyglucose [FDG]) that is given intravenously prior to the procedure. Cancer cells absorb larger amounts of the radioactive substance than normal cells. The areas of higher radioactivity indicate cancerous tissue on the PET scan. Thus, this technique can diagnose spread of disease to distant body parts. It is usually combined with CT scan (PET/CT).
Biopsy samples contain a small number of cells or a tiny piece of tissue collected from the affected area with the help of a biopsy needle. Depending on the size and location of the suspicious area, a fine needle biopsy, a core needle biopsy, or a surgical biopsy technique can be utilized. The biopsy sample is then tested in a laboratory and can provide very useful information about the cancer cells such as the type of cancer (including confirmation of primary bone tumor or any other cancer that has spread to bone), the severity of cancerous changes involved, and the presence of specific defective genes or proteins.
Blood tests can provide certain important information about the diagnosis and prognosis of bone tumor. Serum and urine immunoelectrophoretic analyses can be employed to rule out multiple myeloma. Level of Alkaline phosphatase and lactic dehydrogenase are checked as the level of these enzymes are increased in some cases of bone sarcomas and indicate a worse prognosis.
Now let’s read about treatment of bone tumors.