Key Points

• Staging describes the extent or severity of a person’s cancer. Knowing the stage of disease helps the doctor plan treatment and estimate the person’s prognosis.

• Staging systems for cancer have evolved over time and continue to change as scientists learn more about cancer.

• The TNM staging system is based on the size and/or extent (reach) of the primary tumor (T), whether cancer cells have spread to nearby (regional) lymph nodes (N), and whether metastasis (M), or the spread of the cancer to other parts of the body, has occurred.

• Physical exams, imaging procedures, laboratory tests, pathology reports, and surgical reports provide information to determine the stage of a cancer.

What is staging?

Staging describes the severity of a person’s cancer based on the size and/or extent (reach) of the original (primary) tumor and whether or not cancer has spread in the body. Staging is important for several reasons:

  • Staging helps the doctor plan the appropriate treatment.
  • Cancer stage can be used in estimating a person’s prognosis.
  • Knowing the stage of cancer is important in identifying clinical trials that may be a suitable treatment option for a patient.
  • Staging helps health care providers and researchers exchange information about patients; it also gives them a common terminology for evaluating the results of clinical trials and comparing the results of different trials.

Staging is based on knowledge of the way cancer progresses. Cancer cells grow and divide without control or order, and they do not die when they should. As a result, they often form a mass of tissue called a tumor. As a tumor grows, it can invade nearby tissues and organs. Cancer cells can also break away from a tumor and enter the bloodstream or the lymphatic system. By moving through the bloodstream or lymphatic system, cancer cells can spread from the primary site to lymph nodes or to other organs, where they may form new tumors. The spread of cancer is called metastasis.

All cancers are staged when they are first diagnosed. This stage classification, which is typically assigned before treatment, is called the clinical stage. A cancer may be further staged after surgery or biopsy, when the extent of the cancer is better known. This stage designation (called the pathologic stage) combines the results of the clinical staging with the surgical results.

A cancer is always referred to by the stage it was given at diagnosis, even if it gets worse or spreads. New information about how a cancer changes over time simply gets added on to the original stage designation. The cancer stage designation doesn’t change (even though the cancer itself might) because survival statistics and information on treatment by stage for specific cancer types are based on the original cancer stage at diagnosis.

What are the common elements of staging systems?

Staging systems for cancer have evolved over time. They continue to change as scientists learn more about cancer. Some staging systems cover many types of cancer; others focus on a particular type. The common elements considered in most staging systems are as follows:

  • Site of the primary tumor and the cell type (e.g., adenocarcinoma, squamous cell carcinoma)
  • Tumor size and/or extent (reach)
  • Regional lymph node involvement (the spread of cancer to nearby lymph nodes)
  • Number of tumors (the primary tumor and the presence of metastatic tumors, or metastases)
  • Tumor grade (how closely the cancer cells and tissue resemble normal cells and tissue)