Cancer terminology can sometimes be complex, and confusing. In this explainer we talk about cancer staging and grading. We look at what that means, how it is done, and why knowing the stage and the grade of a cancer can help doctors, and patients.
What are stages and grades in cancer?
Staging and grading are two systems used to classify cancer - where it is growing, and what it looks like. This information helps doctors and patients know how far a cancer has progressed, and how it is likely to grow.
It may require several tests to gather the information needed, which can take time. And the information, when provided, can be difficult to understand. If you have cancer and are struggling with any aspect of your diagnosis, please always reach out to your doctor or another healthcare professional for assistance.
What is the difference between cancer stage and grade?
The stage of a cancer describes how a cancer has grown, its exact location, and how far it has metastasised (spread). The grade of a cancer compares what the cancer cells look like compared to healthy cells.
How does cancer staging work?
Doctors will establish the stage of a cancer based on the results of various routine diagnostic tests, including lab tests, biopsies, and imaging tests such as X-rays or MRI scans.
Different stages of cancer may need very different types of treatment. The information that comes from staging a cancer is also a good predictor of outlook, as cancers diagnosed at an earlier stage are more likely to be treated successfully.
There are many different systems for staging a cancer, but two of the most common systems are the TNM staging system, and the number staging system. We explain both below.
What is the TNM staging system?
A commonly used way to describe lots of different cancers, the TNM staging system uses letters and numbers to explain what stage a cancer is at:
The T score: describes how large the tumour is, usually a score from T1 to T4. The higher the number, the larger and more advanced the tumour is.
The N score: refers to how far the cancer has spread into surrounding lymph nodes. A score between 0 and 3, N0 means that no lymph nodes have been affected, while a higher number means more lymph nodes have been reached.
The M score: describes whether the cancer has metastasised, or spread. Patient are told either that their cancer is M0 (no spread) or M1 (metastasis to one or more different parts of the body).
What is the number staging system?
Cancer can also sometimes be described using a number system, sometimes using Roman numerals. There are four stages of cancer from 1 to 4, and the higher the number, the larger the cancer and the more it has spread.
Stage 1/I: usually an early cancer that is small and has not spread from the organ it started in.
Stage 2/II: a cancer that is larger, but still contained within the organ it started in. It may have started to spread into lymph nodes.
Stage 3/III: a larger cancer again, and it may have also started to spread into surrounding tissues, with cancer cells in nearby lymph nodes.
Stage 4/IV: a cancer that has spread from where it started to another organ in the body, this is also referred to as metastatic or secondary cancer.
Are all cancers given a stage?
No, not every cancer is given a stage. For example, the slow growing skin cancer basal cell carcinoma is not usually staged because it very rarely spreads.
It is also less useful for some blood cancers like leukaemia, because leukaemia is circulated in the blood, and generally does not form solid tumours. Instead leukaemia may be classed as ‘acute’ (more aggressive), or ‘chronic’ (slower-growing).
Brain tumours are also rarely staged, as primary brain tumours (which start inside the brain) do not tend to spread outside of the brain and spinal cord. Instead, brain tumours usually receive a grading, from 1 to 4.
What is the cancer grading system?
Grading a cancer usually requires obtaining a sample of cancer cells. Sometimes this is done by biopsy, where a small part of the cancer is taken for initial examination before any treatment happens. Or, if the cancer is being treated by surgery, sometimes a sample of the cancer removed during surgery is studied under a microscope to find the grade.
Doctors grade a cancer by looking at the sample of the cancer and investigating exactly what the cells look like. The aim is to assess how different they look compared to healthy cells. Cancerous cells usually have a much more disorganised shape and structure than healthy cells, and their internal parts can look different.
Most solid tumours, including breast cancer and prostate cancer, follow a standard grading system from 1 to 3 or 4. The higher the number, the more different the cancer cells appear compared to healthy cells.
What is the cancer grading system?
Low grade/Grade 1: these cancer cells still look quite similar to healthy cells, with only small changes. They are arranged in the tissue similarly to healthy cells.
Intermediate grade/Grade 2: these cancer cells have more obvious changes compared to healthy cells and they might be growing more quickly than normal cells.
High grade/Grade 3 or 4: these cancer cells look very different to healthy cells and have very obviously altered structures and organisation. They may be more likely to spread.
How is research changing how we stage and grade cancer?
Diagnosing a cancer is a bit like painting a picture - the information that comes from staging and grading adds vital detail to the overall image. As international cancer research like ours continues to help improve our understanding of cancer, this in turn helps to make grading and staging systems more accurate.
Diagnosis then becomes easier, quicker, and more detailed, and the picture becomes even more clear.
This is why work by researchers like Professor Kevin Hiom is so important. Thanks to vital Curestarter support, he and his team discovered new genetic information about a rare condition called Fanconi anaemia.
Children with Fanconi anaemia may have developmental disabilities, and are also more likely to develop cancer. An early and accurate diagnosis is really important in helping doctors and families understand how to manage the condition. The information uncovered by Professor Hiom is now helping to improve the diagnosis process, making a real difference to some of these families.
Discovery research will continue to improve treatment options for difficult to treat cancers.
Understanding the molecular and genetic profile of a cancer is increasingly becoming an important part of the staging, grading, and diagnosis process, because the molecular information for each cancer can be very specific and sometimes even differ between people with the same type of cancer.
This helps to explain why some cancers respond better to certain treatments while others do not, and is increasingly being used to help guide some treatment choices. This approach is called personalised treatment, and it is cutting-edge.
As a cancer charity, we are delighted to support Curestarter researchers around the world who are busy discovering new molecular information about cancer. By working out how to use that information to improve diagnosis and personalised medicine we can ultimately develop more effective treatments.
Your cancer staging and grading FAQs:
What is cancer staging and grading?
Cancer staging and grading are ways that healthcare professionals use to describe a patient’s cancer. They both look at how quickly cancer is growing, but in different ways.
The stage of a cancer describes how large a cancer has grown, where it is and whether it has spread. The grade of a cancer compares how the cancer cells look compared to healthy cells.
What are the four stages of cancer?
Cancer is often described using the number staging system which goes from 1 to 4 (or sometimes written in Roman numerals I to IV). The lower the number the smaller the tumour and the less it has spread. Stage 4 or secondary cancer describes a cancer that has spread to another part of the body.
Why are staging and grading important in cancer treatment?
Every cancer is different and so staging and grading are used as ways to predict how any particular cancer might behave, how best to treat it and whether it could potentially be cured.
Do all cancers have a stage and a grade?
No, not all cancers use the standard staging and grading systems. Leukaemia occurs in blood cells growing in bone marrow, so staging works a little differently. Leukaemia stages are based on blood cell counts and how much leukaemia cells appear in other organs.
Brain cancers behave differently to other cancers and usually stay within the brain, so grading is used to describe them but staging is not.
Childhood cancers sometimes have different staging systems because they act differently to cancers in adults.
Do cancer grades affect survival rates or prognosis?
Yes, a lower cancer grade and stage generally implies a slower-growing, less aggressive cancer that is easier to cure. People with lower stages and grades of cancer tend to have better survival rates than people with higher stages and grades.
How are cancer grades and stages used in treatment?
Cancer grades and stages are vital to help provide the best treatment to patients. The stage and grade of a cancer tells a healthcare team how any particular cancer is likely to behave and this information can steer them towards the most suitable treatment plan. A higher grade cancer may grow and spread more quickly, so a more intensive treatment could be recommended.
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