Grade describes how abnormal cells look under the microscope. The pathologist compares the cells in your sample with normal cells from the same tissue. More abnormal-looking cells receive a higher grade.
Pathologists use grade mainly for cancers and precancerous changes. Grade helps predict how fast a cancer may grow. This article explains what grade means, how pathologists assign it, which grading systems exist, and what your report may say.
What does grade mean?
Grade measures how closely abnormal cells resemble the normal cells they came from. Pathologists call this resemblance differentiation. Cells that look much like normal cells are well differentiated. Cells that look very different from normal cells are poorly differentiated. Grade describes the cells. It does not measure how far the cancer has spread.
What are the grades of a cancer?
Most cancers fall into low-, intermediate-, or high-grade. Many systems use numbers. The levels usually match the words pathologists use for differentiation:
- Low grade (grade 1). The cells look similar to normal cells. Pathologists call them well differentiated. The cancer usually grows slowly. See low grade.
- Intermediate grade (grade 2). The cells look more abnormal. Pathologists call them moderately differentiated. The cancer grows at a medium pace.
- High grade (grade 3). The cells look very abnormal. Pathologists call them poorly differentiated. The cancer tends to grow and spread faster.
- Grade 4. Some systems add a fourth level for the most abnormal-looking cells. Pathologists call these cells undifferentiated.
Each cancer type has its own grading rules. A grade 2 breast cancer and a grade 2 kidney cancer use different measures.
What do pathologists look at when they assign a grade?
Pathologists look at several cellular features. Each grading system uses its own mix. The common features are:
- Overall pattern. The pathologist checks whether the cells form structures like the normal tissue, such as glands or tubes.
- The nuclei. The pathologist checks the nuclei’s size, shape, and variation. See nuclear grade.
- Cell division. The pathologist counts dividing cells. See mitotic rate. A high count means the tumor is growing fast.
Which grading systems might my report use?
Many cancers have their own grading system. Your report names the system when it uses one. Some common examples are:
- Nottingham histologic grade. Pathologists use this system for invasive breast cancer. They score tubule formation, nuclear pleomorphism, and mitotic count from 1 to 3 each. The three scores add up to a total from 3 to 9. A total of 3 to 5 is grade 1, 6 to 7 is grade 2, and 8 to 9 is grade 3. See Nottingham histologic grade.
- Gleason grade and score. Pathologists use this system for prostate cancer. They give the two most common patterns a number from 3 to 5. Add the two numbers to get the Gleason score. A score of 6 is low grade, 7 is intermediate grade, and 8 to 10 is high grade. See Gleason grade and Gleason score.
- Kidney cancer grade. Pathologists use the WHO/ISUP nuclear grade, from 1 to 4, for clear cell kidney cancer. Older reports may use the Fuhrman grade.
- Nuclear grade for DCIS. Pathologists grade ductal carcinoma in situ (DCIS) of the breast mainly by the nuclei. The grade runs from 1 to 3, or from low to high.
How does grade apply to precancerous changes?
Pathologists also grade dysplasia, a precancerous change. Dysplasia means the cells look abnormal and disorganized but have not become cancer. Most body sites use two levels:
- Low grade. The cells are mildly abnormal. The risk of progressing to cancer is lower. See low-grade dysplasia.
- High grade. The cells are markedly abnormal and closely resemble cancer cells. The risk of progression is higher. See high grade dysplasia.
Some older reports use three levels: mild, moderate, and severe. Moderate and severe dysplasia together usually match high-grade dysplasia. In the cervix, the same idea appears as LSIL and HSIL.
Some noncancerous conditions also use scoring systems. For example, a kidney transplant biopsy uses the Banff score. These systems measure severity, and each one works differently.
How is grade different from stage?
Grade and stage answer different questions. Grade describes how abnormal the cells look. Stage describes how big the tumor is and how far the cancer has spread. A low-grade cancer can have a high stage. A high-grade cancer can have a low stage. Doctors use both to plan treatment.
Can the grade change?
The grade can differ between a biopsy and a surgical specimen. A biopsy samples only part of a tumor, and different areas can have different grades. When the surgeon removes the whole tumor, the pathologist may find a higher grade. Pathologists generally report the highest grade they see, even if it covers only part of the tumor.
What does grade mean for treatment and outlook?
Doctors use grade to estimate how a cancer may behave. Low-grade cancers usually grow more slowly and are less likely to spread. High-grade cancers can grow and spread faster. Low grade does not mean benign. A low-grade cancer is still cancer and needs medical care.
Grade is only one factor. Doctors also consider the stage, the genetic features of the tumor, your age, and your general health. Together, these shape your prognosis and your treatment plan.
What might my report say about grade?
Reports describe grade in a few standard ways. Each laboratory phrases it a little differently:
- Low, intermediate, or high grade. The report gives the grade in words.
- Grade 1, 2, 3, or 4. The report gives the grade as a number. The report names the grading system when it uses one.
- Well, moderately, or poorly differentiated. The report describes how much the cells resemble normal cells.
- A score. The report may list a score, such as a Gleason score of 3+4=7 or a Nottingham score of 6 out of 9.
- Low- or high-grade dysplasia. The report describes the grade of a precancerous change.
Questions to ask your doctor
- What grade is my tumor or lesion?
- Which grading system did the pathologist use?
- What does my grade mean for how fast the cancer may grow?
- Did the grade change between my biopsy and my surgery?
- What is my stage, and how does it fit with my grade?
- If my report mentions dysplasia, is it low-grade or high-grade?
- What other features of my tumor should I consider along with the grade?
- How does my grade affect my treatment options?
- Do I need any more tests?
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