Cancer stages explained: what stage and grade mean
When someone is diagnosed with cancer, doctors describe its stage - how large it is and how far it has spread. This guide explains the common terms in plain language so a pathology report or a conversation with a doctor is easier to follow. It is general information only.
What does "stage" mean?
The US National Cancer Institute (NCI) defines stage as the extent of a cancer, such as how large the tumour is and whether it has spread (NCI: Cancer Staging). According to NCI, knowing the stage helps a doctor to:
- understand how serious the cancer is and the likely outlook;
- plan the most suitable treatment;
- identify clinical trials that might be an option.
To work out the stage, doctors may use a physical exam, imaging such as x-rays or scans, lab tests and often a biopsy, in which a small sample of tissue is removed and examined under a microscope. NCI notes there is no single test that can diagnose cancer, and a biopsy is often the only way to tell for sure (NCI: How Cancer Is Diagnosed).
The TNM system
NCI describes TNM as the most widely used staging system, and the main one most hospitals use for cancer reporting. Each letter describes one part of the picture:
- T (tumour) - the size and extent of the main, or primary, tumour. TX means it cannot be measured, T0 means it cannot be found, and T1 to T4 describe a larger tumour or one that has grown further into nearby tissue as the number rises.
- N (nodes) - whether cancer is in nearby lymph nodes. N0 means no cancer in nearby nodes; N1 to N3 refer to the number and location of lymph nodes that contain cancer; the higher the number, the more nodes are involved. NX means this cannot be measured.
- M (metastasis) - whether the cancer has spread to other parts of the body. M0 means it has not; M1 means it has. MX means this cannot be measured.
So a report might read something like T3N1M0. Letters such as "a" or "b" can be added for more detail. NCI notes that some cancers use their own staging systems instead, for example brain and spinal cord tumours and blood cancers.
Stage 0 to stage 4
For many cancers, the TNM details are grouped into broader stages, which is how many doctors and nurses talk about them. NCI summarises them like this:
- Stage 0 - abnormal cells are present but have not spread into nearby tissue. This is also called carcinoma in situ. NCI explains it is not cancer, but it may become cancer, which is why it is usually treated.
- Stages 1, 2 and 3 (also written I, II and III) - cancer is present. The higher the number, the larger the tumour and the more it has spread into nearby tissues.
- Stage 4 (IV) - the cancer has spread to distant parts of the body. For many cancers this is also called metastatic cancer - see what is metastatic cancer?
Stages can be divided further, for example 2A or 2B, to give more detail.
Localised, regional and distant
You may also hear a simpler set of words that NCI says is used mostly by cancer registries for statistics:
- In situ - abnormal cells have not spread to nearby tissue.
- Localised - cancer is limited to where it started.
- Regional - cancer has spread to nearby lymph nodes, tissues or organs.
- Distant - cancer has spread to distant parts of the body.
- Unknown - there is not enough information to say.
Why the stage does not change
One point that often surprises people: NCI explains that a cancer is always referred to by the stage it was given at diagnosis, even if it later grows or spreads. New information is added to the original stage rather than replacing it. And when cancer spreads, it keeps its original name - breast cancer that spreads to the lung is still breast cancer, not lung cancer (NCI: Metastatic Cancer).
Stage is not the same as grade
Grade describes how normal or abnormal the cancer cells look under a microscope, while stage describes size and spread. NCI explains that most tumours are graded 1 to 4 (or X if the grade cannot be assessed). Grade 1 cells look closest to normal and tend to grow more slowly; higher grades look more abnormal and are more likely to grow and spread faster (NCI: Tumor Grade). A pathologist decides the grade from a biopsy sample, and different cancers use different grading factors.
Doctors use stage, grade and other information - such as genetic features of the tumour, a person's age and general health - together when planning care. No single number tells the whole story.
Using this information
Staging language can feel overwhelming. It is completely reasonable to ask your doctor to explain your stage and grade in plain words, or to write them down for you. Our list of questions to ask your doctor may help you prepare, and finding trusted support lists places to turn for help. For the basics of how cancer develops and spreads, see what is cancer?, and for the main cancer groups see common types of cancer. The tests used to find the stage are explained in how cancer is diagnosed, and the main approaches to care in types of cancer treatment.
Sources
- National Cancer Institute: Cancer Staging
- National Cancer Institute: Tumor Grade
- National Cancer Institute: How Cancer Is Diagnosed
- National Cancer Institute: Metastatic Cancer
Published and last reviewed: 15 October 2026.
Common questions
What does TNM stand for?
T describes the size and extent of the main tumour, N describes whether cancer is in nearby lymph nodes, and M describes whether the cancer has spread (metastasised) to other parts of the body.
Is stage 0 cancer?
NCI describes stage 0, or carcinoma in situ, as abnormal cells that have not spread into nearby tissue. It is not cancer, but it may become cancer, so it is usually treated.
What is the difference between stage and grade?
Stage describes how large a cancer is and how far it has spread. Grade describes how abnormal the cells look under a microscope, which can suggest how quickly it may grow.
Can a cancer stage go down or change?
NCI explains that a cancer keeps the stage it was given at diagnosis, even if it changes later. New information is added to the original stage rather than replacing it.