© 2005-2012 American Society of Clinical Oncology (ASCO). All rights reserved worldwide.
Staging is a way of describing where the cancer is located, if and where it has spread, and whether it is affecting the functions of other organs in the body. Doctors use diagnostic tests to determine 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 (chance of recovery). There are different stage descriptions for different types of cancer.
One tool that doctors use to describe the stage is the TNM system. This system judges three factors: the tumor itself, the lymph nodes around the tumor, and if the tumor has spread to the rest of the body. The results are combined to determine the stage of cancer for each person. There are five stages: stage 0 (zero) and stages I through IV (one through four). The stage provides a common way of describing the cancer, so doctors can work together to plan the best treatments.
TNM is an abbreviation for tumor (T), node (N), and metastasis (M). Doctors look at these three factors to determine the stage of cancer:
- How large is the primary tumor and where is it located? (Tumor, T)
- Has the tumor spread to the lymph nodes? (Node, N)
- Has the cancer metastasized to other parts of the body? (Metastasis, M)
Tumor. 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. Some stages are also divided into smaller groups that help describe the tumor in even more detail. Specific tumor stage information for bone cancer is listed below.
TX: The primary tumor cannot be evaluated.
T0: 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 is more than one separate tumor in the primary bone site.
Node. The “N” in the TNM staging system stands for lymph nodes, the tiny, bean-shaped organs that 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. Spread to the regional lymph nodes is rare for primary bone cancer.
NX: The regional lymph nodes cannot be evaluated.
N0: The cancer has not spread to the regional lymph nodes.
N1: The cancer has spread to the regional lymph nodes.
Distant metastasis. The “M” in the TNM system indicates whether the cancer has spread to other parts of the body.
MX: Metastasis cannot be evaluated.
M0: The cancer has not metastasized.
M1: There is metastasis to another part of the body.
M1a: There is metastasis to the lung.
M1b: There is metastasis to another organ.
Grade. A cancer may also be graded. The grade describes how much cancer cells look like healthy cells under a microscope. If they look like healthy cells, called well differentiated, the cancer is a low-grade tumor. If they look very little like healthy cells, called poorly differentiated, the cancer is a high-grade tumor. A tumor’s grade is described using the letter “G” and a number. The grade of cancer can help the doctor predict how quickly the cancer will spread. In general, the lower the grade, the better the prognosis.
GX: The tumor grade cannot be identified.
G1: The cancer cells are well differentiated.
G2: The cancer cells are moderately differentiated.
G3: The cancer cells are poorly differentiated.
G4: The cancer cells are undifferentiated.
Cancer stage grouping
Doctors assign the stage of the cancer by combining the T, N, M, and G classifications. In general, patients with the best prognosis have:
- T1 or T2 tumor
- A lower grade tumor (G1 or G2)
- 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
Stage IA: The tumor is low grade (G1 or G2) and 8 cm or smaller (T1). It has not spread to any lymph nodes or other parts of the body (N0, M0).
Stage IB: The tumor is low grade (G1 or G2) and larger than 8 cm (T2). It has not spread to any lymph nodes or other parts of the body (N0, M0).
Stage IIA: The tumor is high grade (G3 or G4) and 8 cm or smaller (T1). It has not spread to any lymph nodes or other parts of the body (N0, M0).
Stage IIB: The tumor is high grade (G3 or G4) and larger than 8 cm (T2). It has not spread to any lymph nodes or other parts of the body (N0, M0).
Stage III: There are multiple high grade (G3 or G4) tumors in the primary bone site (T3), but they have not spread to any lymph nodes or 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, and 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 organ (any G, any T, any N, and M1b).
Recurrent: Recurrent cancer is cancer that comes back after treatment. If there is a recurrence, the cancer may need to be staged again (called re-staging) using the system above.
Used with permission of the American Joint Committee on Cancer (AJCC), Chicago, Illinois. The original source for this material is the AJCC Cancer Staging Manual, Seventh Edition (2010) published by Springer-Verlag New York, www.cancerstaging.net.