What does the stage of a cancer mean?
Stage describes the extent of a cancer. The National Cancer Institute defines it as how large the tumor is and whether it has spread. It is a measure of reach, not of aggressiveness.
Knowing it does three jobs. It tells the doctor how serious the cancer is and what the chances of survival are. It guides the choice of treatment. And it identifies clinical trials that may be options.
How the stage gets worked out
It is not a single test. NCI says a doctor may order x-rays, lab tests, and other tests or procedures to establish it.
Most staging systems include four pieces of information: where the tumor sits in the body, how big it is, whether cancer has reached nearby lymph nodes, and whether it has reached a different part of the body.
There is more than one system. Some, such as TNM, cover many cancer types. Others are specific to one disease. NCI names brain and spinal cord tumors and blood cancers as examples that use different systems entirely, which is why a leukemia diagnosis often comes without a stage number at all.
Reading TNM on a pathology report
TNM is the most widely used system, and NCI says most hospitals use it as their main method of reporting. It usually appears on the pathology report as a string such as T1N0MX or T3N1M0.
- T is the size and extent of the main tumor, also called the primary tumor. T1 through T4 rise with size or growth into nearby tissue. TX means it cannot be measured. T0 means it cannot be found.
- N is the number of nearby lymph nodes that contain cancer. N1 to N3 rise with the number and location involved. N0 means no nearby nodes contain cancer. NX means it cannot be measured.
- M is whether the cancer has spread to distant parts of the body. M0 means it has not. M1 means it has. MX means it cannot be measured.
Letters after a number add detail, such as T3a and T3b.
Why the number never changes later
This point causes real confusion, and NCI is explicit.
A cancer is always referred to by the stage it was given at diagnosis, even if it later gets worse or spreads. New information about how the cancer has changed over time is added to the original stage. The stage does not change, even though the cancer might.
So a person diagnosed at stage II whose cancer later spreads still has stage II disease, now described as recurrent or metastatic. Hearing "stage II" years on is not the team being out of date. Our guide to cancer staging covers the systems in more depth, and what does TNM staging mean walks through a report line by line.
Two other ways doctors describe it
TNM combinations are usually grouped into five simpler stages. Stage 0 means abnormal cells are present but have not spread to nearby tissue. Stages I, II, and III mean cancer is present, with higher numbers meaning a larger tumor and more growth into nearby tissue. Stage IV means the cancer has spread to distant parts of the body. Letters may follow, so stage 2 prostate cancer may be divided into 2A, 2B, or 2C.
A separate five-category system is used mainly by cancer registries: in situ, localized, regional, distant, and unknown. Unknown means there is not enough information to work out the stage, which is a real category rather than an oversight.
NCI's staging page was last updated on October 14, 2022.
Sources
Want the full picture? Read our complete explanation: Cancer Staging: What the Stage Means
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