What does cancer stage describe?
Stage broadly describes the extent of the cancer in the body. Depending on the cancer, this may include:
- the size of the original tumour;
- how far it has grown into nearby tissues;
- whether nearby lymph nodes are involved;
- whether it has spread to distant organs.
Many solid cancers use a TNM system. T describes features of the original tumour, N describes regional lymph nodes and M describes distant spread. That information may then be grouped into a numbered stage.
The familiar stage 1 to stage 4 system does not work in exactly the same way for every cancer. Blood cancers, brain tumours and some other malignancies use different classifications. Even among cancers that use TNM, the meaning of a particular T or stage group is specific to that cancer.
What does cancer grade describe?
Grade usually describes what the cancer looks like under a microscope and how it is expected to behave. A pathologist examines a biopsy or operation specimen and assesses features such as how different the cells look from the normal tissue and how actively they appear to be dividing.
A lower-grade cancer often looks more like the tissue it arose from and may behave less aggressively. A higher-grade cancer may look more abnormal and may be more likely to grow quickly. These are broad descriptions, not guarantees about what an individual cancer will do.
Grading systems also differ. Some cancers use grade 1 to 3, some include grade 4, and others use named or cancer-specific systems. For prostate cancer, for example, grade groups are derived from the Gleason pattern. Neuroendocrine tumours use differentiation, mitotic activity and markers such as Ki-67.
Does grade 4 mean stage 4?
No. Grade 4 and stage 4 are not interchangeable.
A high-grade cancer can still be confined to the area where it started. A lower-grade cancer can sometimes be found after it has spread. The combination depends on the cancer type and when it was diagnosed.
The same number in two different systems is a common source of confusion. Ask whether the number on a report refers to stage, grade, a T or N category, or another cancer-specific score.
How are stage and grade established?
Stage may be based on examination, scans, biopsies and procedures such as endoscopy. This is often called clinical staging. Surgery can provide additional information about the tumour and lymph nodes, leading to pathological staging.
Grade usually comes from tissue examined by a pathologist. A small biopsy may not always show every part of a tumour, and the final grade can sometimes be refined after surgery.
How do they influence treatment?
Stage helps the team understand where treatment needs to act. A cancer confined to one area may be treated differently from cancer that has spread. Grade can help indicate likely behaviour and whether additional treatment may be useful.
Neither makes the decision alone. Cancer type, molecular or biomarker results, symptoms, previous treatment, general health, performance status and personal priorities may all matter. This is why two people with apparently the same cancer can receive different treatment.
Questions to ask
- Which staging system applies to my cancer?
- Is this a clinical stage or a pathological stage?
- What grading system has been used?
- Which result is most important for the treatment decision?
- Are any biomarker or molecular results also relevant?
Stage and grade are useful summaries, but neither is a complete description of a cancer. Your clinical team can explain the system used for your cancer and what the result means in context.
