What is TNM staging?

by Jason Wasserman MD PhD FRCPC
April 12, 2026

If you have been diagnosed with cancer, your pathology report will almost certainly include a stage. Staging is how doctors describe how far a cancer has grown and whether it has spread beyond where it started. The most widely used staging system in the world is called TNM. Understanding what TNM means — and how to read the letters and numbers in your report — can help you make sense of your diagnosis and have more informed conversations with your care team.

This article explains the TNM staging system in plain language: what each letter stands for, how the stage is determined, what the numbers mean, and how staging affects your treatment and prognosis.

What does TNM stand for?

TNM is an abbreviation for three key pieces of information about a cancer:

• T — Tumor: How large is the primary tumor (the original tumor), and how deeply has it grown into surrounding tissue?
• N — Nodes: Has the cancer spread to nearby lymph nodes? Lymph nodes are small, bean-shaped glands scattered throughout the body that help fight infection. Cancer can spread through the lymphatic system — a network of vessels connecting the lymph nodes — before it reaches other organs.
• M — Metastasis: Has the cancer spread to distant parts of the body, such as the liver, lungs, or bones? This is called metastasis.

Each of these three components is assigned a number. Together, the T, N, and M values are combined to give an overall stage — usually expressed as Stage I, II, III, or IV. Lower stages mean the cancer is more localized; higher stages mean it has spread further.

Who assigns the TNM stage?

The TNM stage can be assigned in two different ways, and your report may include one or both:

• Clinical stage (cTNM) — Assigned before surgery, based on physical examination, blood tests, and imaging studies such as CT scans, MRI, or PET scans. This is an estimate of the cancer’s extent based on what can be seen without directly examining the tumor tissue.
• Pathologic stage (pTNM) — Assigned after surgery, when the removed tumor and any lymph nodes are examined under the microscope by a pathologist. Because the pathologist can directly measure the tumor, assess its depth of invasion, and count the number of lymph nodes containing cancer cells, the pathologic stage is generally more accurate than the clinical stage. The lowercase “p” before the letters signals that the information came from this direct tissue examination.

Most pathology reports you receive after surgery will include a pTNM stage. If you had imaging and biopsies before surgery, your oncologist may have also assigned a clinical stage at an earlier point in your care.

What do the T, N, and M numbers mean?

Tumor stage (T)

The tumor stage describes the size and local extent of the primary tumor — that is, how large it is and how far it has grown into nearby tissues. The exact criteria vary depending on the type of cancer, but the general pattern is consistent across most cancers:

• TX — The primary tumor cannot be assessed because there is not enough information.
• T0 — No evidence of a primary tumor. This can occur when a cancer is found in lymph nodes or elsewhere, but the original tumor has disappeared or cannot be found.
• Tis — Cancer cells are present but have not yet grown beyond the surface layer of the tissue where they started. This is sometimes called “in situ” disease. It is the earliest possible stage and is generally not yet invasive.
• T1 — The tumor is small and/or limited to the organ or tissue where it started. The exact size cutoff depends on the cancer type.
• T2 — The tumor is larger or has grown slightly beyond its starting point but remains relatively confined.
• T3 — The tumor is larger still, or has grown into nearby structures outside the organ of origin.
• T4 — The tumor has grown extensively into surrounding organs or structures. T4 cancers are often considered locally advanced.

Many cancer types also use subdivisions such as T1a, T1b, T2a, and T2b to capture finer distinctions in size or extent. Your pathology report will explain the specific criteria that apply to your cancer type.

Nodal stage (N)

The nodal stage describes whether cancer has spread to nearby (regional) lymph nodes and, if so, how many nodes are involved. Finding cancer in lymph nodes is significant because it indicates the cancer is beginning to spread beyond its starting point.

• NX — The regional lymph nodes cannot be assessed.
• N0 — No cancer found in the regional lymph nodes.
• N1 — Cancer is present in a small number of nearby lymph nodes, or in one specific group of nodes near the tumor.
• N2 — Cancer is present in more lymph nodes, or in nodes farther from the tumor.
• N3 — Cancer is present in a larger number of lymph nodes, or has spread to more distant regional node groups.

Not all cancers use N1, N2, and N3 — some use only N0 and N1. The definitions for each nodal stage also differ by cancer type. Your pathology report will tell you exactly how many lymph nodes were examined and how many contained cancer cells.

In some cases, your report may also mention extranodal extension — a finding that means cancer cells have broken through the outer wall of a lymph node into the surrounding tissue. Extranodal extension is associated with a higher risk of recurrence and may influence treatment decisions.

Metastasis stage (M)

The metastasis stage describes whether the cancer has spread to distant organs or tissues — for example, from a colon cancer to the liver, or from a lung cancer to the brain.

• M0 — No evidence of distant spread.
• M1 — The cancer has spread to one or more distant sites. Many cancers further subdivide M1 (for example, M1a, M1b, M1c) depending on where the spread has occurred and how extensive it is.

The M category is usually determined by imaging studies — CT, MRI, or PET scan — rather than by pathology alone. Your pathologist may assign M0 or indicate that distant metastasis cannot be assessed from the tissue sample alone. Your oncologist combines the pathology findings with imaging results to assign a final M stage.

How is the overall stage determined?

Once the T, N, and M values are known, they are combined using a standardized table to produce an overall stage — typically Stage I through Stage IV. This overall stage is a shorthand summary of how far the cancer has progressed:

• Stage I — The cancer is localized and small. It has not spread to lymph nodes or distant organs.
• Stage II — The cancer is larger or has grown more deeply into surrounding tissue, but spread to lymph nodes or distant organs is limited or absent.
• Stage III — The cancer has spread to nearby lymph nodes or has grown into adjacent structures. It has not yet spread to distant organs.
• Stage IV — The cancer has spread to distant organs or tissues. This is also called metastatic disease.

The exact boundaries between stages differ significantly by cancer type. A T2N1M0 colon cancer and a T2N1M0 breast cancer are not the same disease and do not carry the same prognosis. Always refer to your care team or the diagnosis-specific guides on this site for the staging criteria that apply to your cancer.

Which staging system does my pathology report use?

Most pathology reports in North America and internationally follow the TNM criteria published by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC). These two organizations jointly publish the TNM criteria, which are updated periodically as new evidence emerges. The current standard is the 8th edition, which has been in use since 2018. You may see this referenced in your report as “AJCC 8th edition.”

A small number of cancer types — particularly blood cancers such as leukemia and lymphoma — use different staging systems that are specific to those diseases. If your report does not use TNM staging, your oncologist will explain the staging system that applies to your diagnosis.

What does the stage mean for treatment and prognosis?

The TNM stage is one of the most important factors your care team uses when planning treatment. A lower stage generally means more treatment options are available and that the goal of treatment is more likely to be cure. A higher stage may mean that controlling the cancer and managing symptoms becomes a greater focus, though many people with advanced-stage cancers do respond to treatment and live for years.

Stage also influences prognosis — the likely outcome of the disease over time. Survival statistics published in medical literature are almost always organized by stage. However, these statistics describe averages across large groups of people and cannot predict what will happen in any individual case. Many factors beyond stage — including the specific cancer type, its molecular features, your overall health, and the treatments available — also affect outcomes.

If you have questions about what your specific stage means for your treatment options and prognosis, your oncologist is the best person to ask.

Can the stage change?

Yes. A clinical stage assigned before surgery may be revised once the surgical specimen is examined. This is called upstaging (when the pathologic findings reveal more disease than imaging suggested) or downstaging (when the findings reveal less disease). Downstaging can also occur intentionally, when treatment given before surgery — such as chemotherapy or radiation — reduces the size and extent of the cancer. This is called neoadjuvant treatment, and when it works well, the tumor may shrink significantly before the surgeon removes it.

After treatment, the stage assigned at the time of initial diagnosis generally remains the reference point for your medical record. A new or recurrent cancer that develops later would be staged separately.

Questions to ask your doctor

• What is my TNM stage, and what does each part — T, N, and M — mean for my specific cancer?
• Is the stage in my pathology report a clinical stage (cTNM) or a pathologic stage (pTNM)?
• Did the pathologic stage change after surgery compared to the clinical stage I was assigned before the operation?
• How many lymph nodes were examined, and how many contained cancer?
• Was extranodal extension found in any of the lymph nodes?
• Is there any evidence of distant spread (M1), and how was this determined?
• What overall stage (I, II, III, or IV) does my TNM combination translate to?
• How does my stage affect my treatment options?
• What is the prognosis typically associated with my stage for this cancer type?
• Will my stage be reassessed after treatment, and if so, how?
• Are there clinical trials I should consider based on my stage?
• Where can I find reliable information about the staging criteria for my specific cancer?