Tumor Grades and Breast Cancer

Determining the aggressiveness of a tumor helps stage it

There are many factors that are used to determine cancer prognosis and treatment planning, and cancer stage is among the most important. Part of defining the stage is knowing what the tumor grade is.

Tumor grade is one aspect of a pathology report. The grade is a description of how abnormal the cancer cells look when they are examined with a microscope. This information can be used by an oncologist to estimate how likely it is for the tumor to grow and spread.

This article will review the grading of tumors and how it impacts treatment decision-making.

doctor looking at MRI results of tumors
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Why Breast Cancer Is Graded

A breast biopsy sample can be used to determine the cancer type, grade, and stage.

Cancer staging and cancer grading are often related, but they are not the same.

  • Cancer staging refers to the size or extent of a solid tumor and whether or not it has spread to other organs and tissues. It takes into account multiple factors to establish how serious your cancer is and which treatments are best suited for you. Cancer stages are classified from stage 0 (very early stage) to stage IV (metastatic cancer).
  • Cancer grading evaluates how normal or abnormal the cancer cells look when they are examined with a microscope. This can help predict how fast a tumor is likely to spread.

Cancer grading is part of breast cancer staging and is an indicator of the the aggressiveness of breast cancer. Breast cancer staging is not solely based on the grade of the tumor. Other factors include the size and location of the tumor, the number of lymph nodes affected, and the degree of metastasis (spread).

How a Breast Cancer Grade Is Determined

The Nottingham grading system is the grading system used specifically for breast cancer.

This system uses three features to determine the grade of the breast cancer.

  • The percentage of normal ducts in the tumor specimen (tubule formation)
  • How many cells are in the process of dividing in the tumor specimen (mitotic rate)
  • How the nucleus of the cell looks (nuclear grade)

For each of the three criteria, the cells are given a number between 1 and 3. A score of 1 means the cells look more like normal cells, while a 3 means they look very abnormal. The scores are added to give a total number between 3 and 9.

Low-grade tumors, which are more similar to normal cells, tend to grow slowly and have a grade of 3-5. High-grade tumors are more abnormal-looking and spread quickly, and have a grade of 8-9.

Tubule Formation

This refers to how much of the tumor tissue has normal breast (milk) ducts. Scoring is as follows:

Tubule Formation Score Indication
1 Greater than 75% of cells are normal
2 Between 10% and 75% are normal
3 Less than 10% are normal

Mitotic Rate

This refers to the quantity of mitotic (dividing) cells seen with 400 times microscopic magnification. Scoring is as follows:

Mitotic Rate Score Indication
1 Fewer than 10 mitotic cells were seen
2 Between 10 to 19 mitotic cells were seen
3 At least 20 mitotic cells were seen

Nuclear Grade

This is the evaluation of the size and shape of the nucleus in tumor cells. The scoring system:

Nuclear Grade Score Indication
1 Nuclei are small and uniform
2 There are intermediate variations in size and shape
3 There are marked variations

Final Tumor Grade Determination

The three scores are combined to determine the grade of the tumor. When a grade is higher, it is more aggressive and is more likely to spread.

Total Feature Score Tumor Grade Appearance of Cells
3 to 5 Grade 1 tumor Well differentiated (appear normal, growing slowly, not aggressive)
6 to 7 Grade 2 tumor Moderately differentiated (semi-normal, growing moderately quickly)
8 to 9 Grade 3 tumor Poorly differentiated (abnormal, growing quickly, aggressive)

If breast cancer is found to be high grade, it may require more intense therapy, such as a combination of surgery, chemotherapy, and radiation.

Summary

A tumor's grade is a rating of how it looks when viewed with a microscope—it is based on whether the tumor cells look like more like normal or abnormal cells. The grade can predict the tumor's aggressiveness and likelihood of spreading, and it is one of the criteria used to determine the cancer's stage. The stage is an important factor in determining the treatment plan and prognosis for the cancer.

Breast Cancer Discussion Guide

Get our printable guide for your next healthcare provider's appointment to help you ask the right questions.

Doctor Discussion Guide Woman

Frequently Asked Questions

  • How many grades of breast cancer are there?

    There are three grades of breast cancer—grades 1, 2, and 3—with higher numbers indicating more aggressive and abnormal cancer cells. The grade is based on three factors: tubule formation, mitotic rate, and nuclear grade. Each of these gets a score from 1 to 3, and the scores are totaled to determine the final grade.

  • Is grade 2 breast cancer curable?

    It may be. Compared to grade 3 breast cancer, grade 2 tends to be less aggressive and slower growing, and may be more likely to be cured.

Originally written by
Pam Stephan
Pam Stephan is a breast cancer survivor.
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  1. Guiliano A, Connolly J, Edge S, et al. Breast cancer—Major changes in the American Joint Committee on Cancer 8th edition cancer staging manual. CA: Cancer J Clinician. 2017;67(4):290-303: doi:10.3322/caac.21393

  2. National Cancer Institute. Tumor grade.