Grading breast cancer

The grade is a description of how the cancer cells look compared to normal cells. To find out the grade of breast cancer, the pathologist looks at a tissue sample from the tumour under a microscope. The pathologist will also look at specific features of the cancer cells to give breast cancer a grade from 1 to 3. A lower number means the cancer is a lower grade.

How different the cancer cells are is described as differentiation.

Low grade means the cancer cells are well differentiated. They look almost like normal cells. Lower grade cancer cells tend to be slow growing and are less likely to spread.

High grade means that the cancer cells are poorly differentiated or undifferentiated. They look less normal, or more abnormal. Higher grade cancer cells tend to grow more quickly and are more likely to spread than low-grade cancer cells.

Knowing the grade gives your healthcare team an idea of how quickly the cancer may be growing and how likely it is to spread. This helps them plan your treatment. The grade can also help the healthcare team predict your prognosis and how the cancer might respond to treatment.

The most common grading system for breast cancer that has spread to surrounding tissues (called invasive breast cancer) is based on 3 features of the cells in the tumour that make them different from healthy cells:

• Tubule formation describes the percentage of cells in the tumour that have tube-shaped structures (called tubules).
• Nuclear pleomorphism describes how different the nucleus of each cancer cell is from normal cells.
• Mitotic count is the number of cells in the tumour that are actively dividing.

The pathologist gives each feature a score of 1 to 3 and then adds them to determine the grade.

The grade for DCIS is based on the differentiation of the cancer cells, what the nucleus in each cancer cell looks like and if there are dead or dying cancer cells (called necrosis) in the sample from the tumour.