Tumor grade is a way of classifying tumors based on certain features of their cells. The grade of a tumor is directly linked to prognosis. Using a microscope, a pathologist studies the tissue taken during a biopsy to see how much the cancer cells look like normal cells. The more the cells look like normal cells, the lower (or better) the tumor grade. The pathologist also checks to see how many of the cancer cells are in the process of dividing. The fewer cells that are dividing, the slower the tumor is likely growing and the lower the tumor grade. Together, these factors determine the grade of a tumor.
The prognosis is worse for a person who has a tumor with the same size and stage, but a higher tumor grade (see Figure 4.5). A tumor whose cells look like normal tissue and are slow-growing will most often be classified as Grade 1 (well-differentiated). A tumor whose cells look abnormal and are fast-growing will most often be classified as Grade 3 (poorly-differentiated). Cells that fall somewhere in between are classified as Grade 2 (moderately-differentiated).
Figure 4.5: Tumor Grade and Rate of Distant Recurrence within 10 Years in Women Treated with Lumpectomy plus Radiation between 1970 and 1986 for Stage I and II Breast Cancer*
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Grade
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Distant Recurrence
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Grade 1 (Well-differentiated)
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15%
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Grade 2 (Moderately-differentiated)
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26%
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Grade 3 (Poorly-differentiated)
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29%
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*This study combined all types of stage I and stage II breast cancers and presented recurrence rates by grade. However, many other factors have a large impact on recurrence. If you have a grade I breast cancer, for example, your chances of recurrence will be greatly affected by these other factors.
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Nixon et al., 1996 [16]
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Updated 10/26/09
