Bone Cancer: Stages and Grades

Approved by the Cancer.Net Editorial Board, 11/2018

ON THIS PAGE: You will learn about how doctors describe a cancer’s growth or spread, as well as the way the tumor cells look when viewed under a microscope. This is called the stage and grade. Use the menu to see other pages.

Staging is a way of describing where the cancer is located, if and where it has spread, and whether it is affecting other parts of the body.

Doctors use diagnostic tests to find out the cancer's stage, so staging may not be complete until all of the tests are finished. Knowing the stage helps the doctor to decide what kind of treatment is best and can help predict a patient's prognosis, which is the chance of recovery. There are different stage descriptions for different types of cancer.

TNM staging system

One tool that doctors use to describe the stage is the TNM system. Doctors use the results from diagnostic tests and scans to answer these questions:

  • Tumor (T): How large is the primary tumor? Where is it located?

  • Node (N): Has the tumor spread to the lymph nodes? If so, where and how many?

  • Metastasis (M): Has the cancer spread to other parts of the body? If so, where and how much?

The results are combined to determine the stage of cancer for each person. In most primary bone cancers, there are 5 stages: stage 0 (zero) and stages I through IV (1 through 4). The stage provides a common way of describing the cancer, so doctors can work together to plan the best treatments.

Here are more details on each part of the TNM system for bone cancer:

Tumor (T)

Using the TNM system, the “T” plus a letter or number (0 to 4) is used to describe the size and location of the tumor. Tumor size is measured in centimeters (cm). A centimeter is roughly equal to the width of a standard pen or pencil.

Stages may also be divided into smaller groups that help describe the tumor in even more detail. Specific tumor stage information for bone cancer is listed below.

Skeleton, trunk, skull, and facial bones

TX: The primary tumor cannot be evaluated.

T0 (T plus zero): There is no evidence of a primary tumor.

T1: The tumor is 8 centimeters (cm) or smaller.

T2: The tumor is larger than 8 cm.

T3: There are more than 1 separate tumors in the primary bone site.

Spine

TX: The primary tumor cannot be evaluated.

T0 (T plus zero): There is no evidence of a primary tumor.

T1: The tumor is found only on 1 part of the vertebrae, called the vertebral segment, or on 2 adjacent parts of the vertebrae.

T2: The tumor is found only on 3 adjacent parts of the vertebrae.

T3: The tumor is found on 4 or more adjacent parts of the vertebrae, or it is found on parts of the vertebrae that are not next to each other.

T4: The tumor has grown into the spinal canal or great vessels.

  • T4a: The tumor has grown into the spinal canal.

  • T4b: The tumor has grown into the great vessels or affects blood flow.

Pelvis

TX: The primary tumor cannot be evaluated.

T0 (T plus zero): There is no evidence of a primary tumor with no extraosseous extension.

T1: The tumor is located only on 1 part of the pelvis.

  • T1a: The tumor is 8 cm or smaller.

  • T1b: The tumor is larger than 8 cm.

T2: The tumor is located only on 1 part of the pelvis with extraosseous extension or on 2 parts of the pelvis without extraosseous extension.

  • T2a: The tumor is 8 cm or smaller.

  • T2b: The tumor is larger than 8 cm.

T3: The tumor is found on 2 parts of the pelvis with extraosseous extension.

  • T3a: The tumor is 8 cm or smaller.

  • T3b: The tumor is larger than 8 cm.

T4: The tumor is found on 3 parts of the pelvis or it has crossed the sacroiliac joint, which connects the bottom of the spine with the pelvis.

  • T4a: The tumor involves the sacroiliac joint and has grown to the sacral neuroforamen.

  • T4b: The tumor has grown around blood vessels or affects blood flow.

Node (N)

The “N” in the TNM staging system stands for lymph nodes. These tiny, bean-shaped organs help fight infection. Lymph nodes near where the cancer started are called regional lymph nodes. Lymph nodes in other parts of the body are called distant lymph nodes.

NX: The regional lymph nodes cannot be evaluated.

N0 (N plus zero): The cancer has not spread to the regional lymph nodes.

N1: The cancer has spread to the regional lymph nodes. This is rare for primary bone cancer.

Metastasis (M)

The “M” in the TNM system describes whether the cancer has spread to other parts of the body, called distant metastasis.

M0 (M plus zero): The cancer has not metastasized.

M1: The cancer has metastasized to another part of the body.

  • M1a: The cancer has metastasized to a lung.

  • M1b: The cancer has metastasized to other bones or another organ.

Grade (G)

Doctors also describe this type of cancer by its grade (G). The grade describes how much cancer cells look like healthy cells when viewed under a microscope.

The doctor compares the cancerous tissue with healthy tissue. Healthy tissue usually contains many different types of cells grouped together. If the cancer looks similar to healthy tissue and has different cell groupings, it is called "well differentiated" or a "low-grade tumor." If the cancerous tissue looks very different from healthy tissue, it is called "poorly differentiated" or a "high-grade tumor." The cancer’s grade may help the doctor predict how quickly the cancer will spread. In general, the lower the tumor’s grade, the better the prognosis.

GX: The 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).

Cancer stage grouping

Doctors assign the stage of the cancer by combining the T, N, M, and G classifications. There are no stage groupings for primary bone cancer in the spine or pelvis.

Stage IA: The tumor is low grade or cannot be graded (G1 or GX) and 8 cm or smaller (T1). It has not spread to any lymph nodes or to other parts of the body (N0, M0).

Stage IB: The tumor is low grade or cannot be graded (G1 or GX) and larger than 8 cm (T2) or there are more than 1 separate tumors in the primary bone site (T3). It has not spread to any lymph nodes or to other parts of the body (N0, M0).

Stage IIA: The tumor is high grade (G2 or G3) and 8 cm or smaller (T1). It has not spread to any lymph nodes or to other parts of the body (N0, M0).

Stage IIB: The tumor is high grade (G2 or G3) and larger than 8 cm (T2). It has not spread to any lymph nodes or to other parts of the body (N0, M0).

Stage III: There are multiple high-grade (G2 or G3) tumors in the primary bone site (T3), but they have not spread to any lymph nodes or to other parts of the body (N0, M0).

Stage IVA: The tumor is of any size or grade and has spread to the lung(s) (any G, any T, N0, M1a).

Stage IVB: The tumor is of any size or grade and has spread to the lymph nodes (any G, any T, N1, and any M), or the tumor is of any size or grade and has spread to another bone or organ besides the lung (any G, any T, any N, M1b).

Recurrent: Recurrent cancer is cancer has come back after treatment. If the cancer does return, there will be another round of tests to learn about the extent of the recurrence. These tests and scans are often similar to those done at the time of the original diagnosis.

In general, patients with the best prognosis have:

  • A T1 or T2 tumor

  • A low-grade tumor (G1)

  • A tumor that is easily removed with surgery, such as those located in an arm or leg

  • A localized tumor that has not spread

  • Certain genetic changes

Used with permission of the American College of Surgeons, Chicago, Illinois. The original and primary source for this information is the AJCC Cancer Staging Manual, Eighth Edition (2017), published by Springer International Publishing.

Information about the cancer’s stage and grade will help the doctor recommend a specific treatment plan. The next section in this guide is Types of Treatment. Use the menu to choose a different section to read in this guide.