What is Tumor Staging and Why is it Important?

What is Tumor Staging?

The staging of a tumor is undertaken based on several characteristics of the tumor, such as its size, spread and cellular abnormalities, within the tumor. Staging helps classify a cancer, and allows a healthcare provider to make the following decisions:

  • Understand the seriousness of the cancer and make an informed prediction on prognosis
  • Plan the most appropriate treatment
  • Identify clinical trials that may be applicable in treating an individual

The stage assigned at diagnosis is always used to refer to a cancer regardless of subsequent spreading or advancement of the tumor. In other words, over time, as new information gathered about the tumor and its progression is added to the original stage, the stage does not usually change.

Determination of Tumor Stage:

To determine the stage of a tumor, a healthcare provider may order lab tests, X-rays, or other procedures depending on each individual case.

Cancer staging can be categorized into clinical stage and pathologic stages. 

The clinical staging is performed before the tumor is removed. The healthcare professional may use a variety of tools, such as blood test, imaging studies (such as Ultrasound scans, Computed Tomography or CT scans, Magnetic Resonance Imaging or MRI scans, Positron Emission Tomography or PET scans, and Bone scans) and physical examination. 

The pathologic staging is performed when the pathologist examines the tumor tissue after the surgery.

In general, the pathologic stage is more accurate than clinical stage. However, since the two staging systems use different methods, they may differ frequently. In many cases, the information derived from the two staging methods complement each other. 

Sometimes, treatments such as radiation therapy or chemotherapy are initiated before surgery. This may result in “under-staging“ of the pathological staging, when subsequent surgery to remove the tumor is performed. On other occasions, a surgery may not be performed to remove the tumor. In such cases there is no pathological staging and the treatment is based solely on the clinical staging.

Systems for Designating Tumor Stage:

Many staging systems, such as the TNM staging system, are used to classify various types of cancers. Certain other staging systems are designed to stage a specific type of cancer. The information used in most staging systems include: 

  • The location of the tumor in the body
  • The type of cell in the tumor (i.e., adenocarcinoma, squamous cell carcinoma, etc.)
  • The tumor size
  • If the cancer has spread to nearby lymph nodes
  • Whether the cancer has metastasized to other parts of the body
  • The grade of the tumor based on how abnormal cells appear, and the likelihood of the tumor to spread and grow

The TNM Staging System:

The TNM system is the most common cancer staging system used by many hospitals and medical centers as their main method for cancer reporting. Their typical pathology reports will very likely use the TNM system for describing cancers. Staging systems other than TNM are used to describe tumors of the brain and spinal cord, as well as blood cancers.

The TNM system includes the following components:

  • The letter T is used to describe the size and extent of the primary or main tumor
  • The letter N represents the number of lymph nodes near the primary tumor that have cancer
  • The letter M indicates whether the cancer has metastasized. Metastasis refers to the cancer spreading from the primary tumor to other parts of the body

Cancers described by the TNM system have numbers after each letter to give more detail about the cancer. Such examples include T1N0MX or T3N1M0. The explanation for letters and numbers are given below: 

Primary Tumor (T)

  • TX: Main tumor is unable to be measured
  • T0: The main tumor cannot be found
  • T1, T2, T3, T4: This refers to the size or level of extent of the main tumor. As numbers following T increase, the larger is the tumor size, and the more it has developed into the nearby tissues. T’s can be described more specifically by adding more information after the number such as T2a or T2b

Regional Lymph Nodes (N)

  • NX: Cancer in nearby lymph nodes is unmeasurable
  • N0: No cancer is present in nearby lymph nodes
  • N1, N2, N3: Refers to the location and number of nearby lymph nodes that contain cancer. The higher the number following N, the more are the nearby lymph nodes that contain cancer

Distant Metastasis (M)

  • MX: Metastasis is unmeasurable
  • M0: The cancer has not spread to other parts of the body
  • M1: Cancer has spread to distant parts of the body

Other Methods to Describe Stage:

The TNM system gives a very detailed description of the cancer, but for many cancers, TNM groupings can be split into five 'less' detailed stages. A medical professional is likely to use these stages when describing cancer to an individual with a tumor:

Stage Description of Stage
Stage 0Abnormal cells are present, but have not spread to the nearby tissues. This is commonly referred to as carcinoma in situ or CIS, which is not cancer, but may develop into cancer later on.
Stage I, Stage II, and Stage IIICancer is existent. The higher the stage, the larger the tumor is, and the more it has spread to nearby tissues.
Stage IVThe cancer is present in distant parts of the body in relation to the primary tumor.


Along with the TNM staging system, there is another system which is used for all types of cancer. This staging system divides the cancer into one of 5 main groups. Although this  method is not typically used by medical practitioners, it is commonly used by cancer registries. The cancer can be described in the following ways:

  • In situ - Abnormal cells are present, but have not spread to nearby tissues
  • Localized - The cancer is restricted to the place of origin with no sign of spreading
  • Regional - Cancer has spread to the nearby tissues, lymph nodes, or organs
  • Distant - Spreading of cancer has occurred to distant parts of the body
  • Unknown - Not enough information is known to determine stage

References:

https://www.cancer.gov/about-cancer/diagnosis-staging/staging (accessed on 3/17/2017)

https://www.cancer.org/treatment/understanding-your-diagnosis/staging.html (accessed on 3/17/2017

https://cancerstaging.org/references-tools/Pages/What-is-Cancer-Staging.aspx (accessed on 3/17/2017)

Peer-Reviewed Medical Articles:

Edge, S. B., & Compton, C. C. (2010). The American Joint Committee on Cancer: the 7th edition of the AJCC cancer staging manual and the future of TNM. Annals of surgical oncology, 17(6), 1471-1474.

Greene, F. L., & Sobin, L. H. (2009). A worldwide approach to the TNM staging system: collaborative efforts of the AJCC and UICC. Journal of surgical oncology, 99(5), 269-272.

Ludwig, J. A., & Weinstein, J. N. (2005). Biomarkers in cancer staging, prognosis and treatment selection. Nature Reviews Cancer, 5(11), 845-856.

Webber, C., Gospodarowicz, M., Sobin, L. H., Wittekind, C., Greene, F. L., Mason, M. D., ... & Groome, P. A. (2014). Improving the TNM classification: Findings from a 10‐year continuous literature review. International journal of cancer, 135(2), 371-378.