What are the stages of bone cancer?

After diagnosis, doctors will set about to determine the stage of the bone cancer. The process of trying to find out the severity and spread of cancer is known as staging. This further helps in understanding how serious it is and how better to treat cancer.

There are four cancer stages from I (1) through IV (4). By rule, the lower the number, the lower the spread of cancer. Although each patient has individual differences, approaches to a certain stage of cancer are by and large similar and usually treated in a similar manner.

How is the Stage of Cancer Determined?

Doctors use diagnostic tests to determine the stage and spread of cancer. Knowing the stage helps them best predict the prognosis, treatment and determining the chance for recovery.

The staging system mostly used is the American Joint Committee on Cancer (AJCC) TNM method. This method is primarily based on 4 primary pieces of information:

1. The extent (size) of the tumor (T):

This indicates how large the cancer is and if it has affected more bones than one.

2. The spread of nearby lymph nodes (N):

This determines if the cancer has spread to the lymph nodes.

3.The metastasis or the spread of the cancer to distant site (M):

This indicates if the cancer has spread to either the lungs alone or distant sites such as the liver.

4.The grade of the cancer (G):

The determines how abnormal the cells appear when viewed under a microscope. The grading scale for bone cancer is from 1 to 3. Low-grade (G1) cancers grow and spread slower than high-grade (G2 or G3) cancers.

Numbers or letters after initials T, N, and M help understand the factors that determine the stage of the cancer.

Tumor:

The ‘T’ in the TNM system indicates the size and the location of the cancer. Some stages are further classified into sub-stages as in the following:

Skeleton, trunk, skull, and facial bones have the following groups:

TX: the primary tumor cannot be evaluated
T0: there still is no evidence of the primary tumor
T1: the tumor is 8 cm or smaller
T2: the tumor is larger than 8 cm
T3: there are more than 1 separate tumors in the primary site

Spine:

TX: the primary tumor cannot be evaluated
T0: There is no evidence of primary tumor
T1: tumor is only found on one part of the vertebra, called the vertebral segment, or on 2 adjacent parts of the vertebrae
T2: tumor is found only on 3 adjacent parts of the vertebrae
T3: tumor is found on 4 or more nearing parts of the vertebrae, or in parts of the vertebrae that are not next to each other
T4: tumor has grown into the spinal canal (T4a) or great vessels (T4b)

Pelvis:

TX: the primary tumor cannot be evaluated
T0: there is no evidence of primary tumor with no extraosseous extension
T1: tumor is only found on one part of the pelvis; where the tumor is 8 cm or smaller (T1a) or tumor is larger than 8 cm (T1b)
T2: tumor is found only on 1 part of the pelvis with extraosseous extension or on 2 parts of the pelvis with extraosseous extension; where the tumor is 8 cm or smaller (T2a) or tumor is larger than 8 cm (T2b)
T3: tumor is found on 2 parts of the pelvis, with extraosseous extension; where the tumor is 8 cm or smaller (T3a) or tumor is larger than 8 cm (T3b)
T4: tumor is found on 3 parts of the pelvis or has crossed the sacroiliac joint, which connects the bottom of the spine with the pelvis; where the tumor involves the sacroiliac joint and has grown into the neural foramen (T4a) or the tumor has grown around blood vessels or affects blood flow (T4b)

Node:

The ‘N’ in the TNM system expands to lymph nodes. These are tiny, bean-shaped organs help fight infection and help in immunity. Lymph nodes near the cancer are called regional lymph nodes and those that are away from the site are called distant lymph nodes. The following are sub-stages of N grades:

NX: the regional lymph nodes cannot be evaluated
N0: the cancer has not spread to regional lymph nodes
N1: the cancer has spread to regional lymph nodes and this is rare for primary bone cancer

Metastasis:

The ‘M’ in the TNM system indicates the spread of the cancer to other body parts, that are distant.

M0: the cancer has not yet metastasized
M1: the cancer has metastasized to other body parts; where when it has metastasized to the lungs it is M1a or to other bones and organs it is M1b

Grade

Doctors also describe bone cancer by its grade (G) which indicates their health when viewed under a microscope. Doctors compare the cancer tissue to healthy tissue. The lower the tumor grade the better the prognosis. The following are the sub-stages:

GX: tumor grade cannot be identified
G1: the cancer cells are well differentiated (low-grade)
G2: the cancer cells are moderately differentiated (high-grade)
G3: the cancer cells are poorly differentiated (high-grade)

The Number Stages

The tumor, node and metastasis are put together with the grading and given number stages.

Stage 0: This is also known as carcinoma in situ. Detections in this early stage show that it is small, low-grade and has not spread.

Stage 1A: This is low-grade tumor which is not larger than 8 cm.

Stage 1B: This is also low-grade tumor but is longer than 8 cm. It can be found in more than one region of the bone.

Stage 2A: This is high-grade tumor which is less than 8 cm across without having affected lymph nodes and without metastasis.

Stage 2B: This is high-grade tumor located in more than one place in the same bone.

Stage 3: This is a high-grade tumor located in more than one place on the same bone.

Stage 4A: This is any size or grade of tumor that has spread to the lung.

Stage 4B: This is of any size or grade and has spread to the lymph nodes or other distant parts of the body.


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