Pathology dictionary

What does grade mean?

Grade is a word pathologists use to describe the difference between abnormal cells and the normal, healthy cells they have replaced.

The most common use for the word grade is to describe the difference between cancer cells and normal, healthy cells. However, pathologists also use the word grade to describe the changes seen in pre-cancerous and non-cancerous medical conditions.

Grade is usually described using numbers to represent different levels. For example a tumour may be given a grade from 1 through 4. Other ways of describing grade include dividing it into two levels, low and high, or by differentiation (see below for more information).

Grade is used to describe cancer cells

Not all cancers look or behave the same. Some types of cancer look very similar to normal, healthy cells while other types of cancer look very different from normal, healthy cells. Pathologists use the word grade is used to describe the difference between the cancer cells and the normal, healthy cells usually found in that area of the body.

Why is this important? Cancers that look and behave similar to normal cells tend to grow slowly and are less likely to spread to other parts of the body. Cancers that look and behave very little like normal cells tend to grow faster and are more likely to spread to other parts of the body. Your doctors will use the cancer grade to predict how the tumour will behave and to plan treatment.

Low and high grade cancer cells

In some areas of the body, pathologists divide grade into two levels – low and high. Cancer cells that look, grow, and behave more like normal, healthy cells are called low grade. In contrast, cancer cells that look, grow, and behave less like normal, healthy cells are called high grade.

Why is this important? High grade cancers are more likely to grow faster and to spread to other parts of the body. Patients with high grade cancers may be offered additional treatment such as radiation therapy or chemotherapy.

Grade is used to describe pre-cancerous diseases

Pathologists also use grade to describe pre-cancerous diseases. In this situation, low grade diseases look more like normal, healthy cells and are less likely to turn into a cancer over time. In contrast, high grade diseases look less like normal, healthy cells and are more likely to turn into a cancer over time if not treated.

Why is this important? A patient with a high grade pre-cancerous disease may be offered additional treatment such as surgery to reduce the risk of developing cancer in the future.​

Differentiation

For some diseases, grade is divided into levels called differentiation. Differentiation is another word pathologists use to compare the abnormal cells with the normal, healthy cells that are usually found in that location.

Here is an example of how grade can be divided into four levels of differentiation:

  • Well differentiated – Well differentiated cells look very similar to the cells normally found in that location.
  • Moderately differentiated – Moderately differentiated cells are clearly abnormal but they still look somewhat like the cells normally found in that location.
  • Poorly differentiated – Poorly differentiated cells are very abnormal looking and may only share some features with the cells normally found in that location. Pathologists often order additional tests such as immunohistochemistry to figure out where the cells started.
  • Undifferentiated – Undifferentiated cells look nothing like normal cells and additional tests such as immunohistochemistry are almost always performed to learn more about the cells and where they started.
How do pathologists decide the grade?

Grade can only be determined after the tissue sample has been examined under the microscope by a pathologist. When describing pre-cancerous or cancerous cells, pathologists look for some of the following features in order to decide the grade:

  • The size and shape of the abnormal cells compared to the normal, healthy cells usually fund in that area of the body.
  • The way the abnormal cells stick together.
  • How many of the abnormal cells are seen dividing to create new cells. The process of creating a new cell is called mitosis.
  • Whether or not there are any large areas of cell death called necrosis.
Grading systems for specific areas of the body

Special systems have been created to grade tumours in some parts of the body. These grading systems are often named after the person who first created them.

Examples of special systems:

  • The Gleason grading system – This system is used to grade cancers of the prostate including adenocarcinoma.
  • The modified Scarff-Bloom-Richardson or Nottingham grading system – This system is used to grade cancers in the breast including ductal carcinoma in situ, invasive ductal carcinoma, and lobular carcinoma.
  • The WHO/ISUP grading system – This system is used to grade cancers of the kidney including clear cell renal cell carcinoma.
  • French Federation of Cancer Centers Sarcoma Group – This system is used to grade a group of cancers called sarcomas. There are many different types of sarcomas and this grading system can be used for most of them.

Grade is used to describe some non-cancerous medical conditions

Pathologists sometimes use the word grade to describe the changes seen in non-cancerous medical conditions. In this situation, grade is used to how far the disease has progressed. The features used to determine the grade will depend on the disease and the area of the body being examined.

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