grading
Meaning of grading: Answers how the cells look, never how far the disease has traveled, which is why the number is so often quoted alone and misread.
Definition of grading
Grading is the pathologist's assessment of how abnormal tumor cells look under the microscope compared with the healthy tissue they arose from. Low-grade cells still resemble their origin and usually behave slowly; high-grade cells have lost that resemblance and tend to grow and spread faster. Each cancer type carries its own grading scheme, so a grade means little until the tumor type is known.
How is grading different from staging?
Grading describes the cells; staging describes the territory. A pathologist assigns the grade by studying tissue under a microscope and judging how disordered the cells and their arrangement have become. Stage comes instead from measurement and imaging: how large the tumor is, whether it has reached lymph nodes, and whether it has traveled further. The two are independent of each other. A small tumor found early can be high grade, and a widely spread tumor can be built from cells that still look fairly orderly. Both matter, and stage usually carries more weight in predicting what happens next.
What is the pathologist actually looking at?
Several features at once, weighted differently for each cancer type. How faithfully the tissue reproduces the structure it should form, whether that means glands, ducts or layers. How irregular and how darkly stained the nuclei have become. How many cells are caught in the act of dividing within a set area. Whether patches have died after outgrowing their blood supply. These observations are scored and added, so a grade is a considered judgment rather than a machine reading, and two pathologists can reasonably differ at the boundaries between categories.
Do all cancers use the same scale?
| Scheme | Applied to | What is scored |
|---|---|---|
| Nottingham system | Breast tumors | Gland formation, nuclear shape, dividing cells |
| Gleason score and grade group | Prostate tumors | The two commonest growth patterns, combined |
| Central nervous system grade | Brain and spinal tumors | Cell appearance together with molecular markers |
| Three or four tier scales | Many other tumors | Overall resemblance to the parent tissue |
These scales do not translate into one another. A middling grade means one thing in a breast cancer report and something quite different in a brain tumor, and the prostate scale historically started at a number well above one, which caused confusion for years until grade groups were introduced. A grade quoted without the cancer type attached carries almost no information.
Also known as
Used in a sentence
Grading of the resected specimen placed the tumor at the high end of the scale for that site.
Good to know
Grade and stage answer different questions and are routinely mixed up: grade reports how abnormal the cells appear, stage reports how far the disease has traveled, and the numbering runs on different scales for different cancers.
Word origin
Where “grading” comes from
Grade descends from the Latin gradus, meaning a step, the same root behind gradual and degree. A grading scheme sets out steps between orderly and disorderly tissue.