Tumor Grades and Breast Cancer

Determining the aggressiveness of a tumor helps stage it

Doctor talking with patient
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Tumor grade is one of many items that will appear on your pathology report if you have breast cancer. It is a description of what the cell looks like under the microscope, the characteristics of which can tell a doctor how likely it is to grow and spread. Knowing the tumor grade can play a key role in helping your doctor decide which course of treatment is most appropriate for you.

Doctors most often use the Nottingham system for grading breast cancer. It is a modification of the Bloom-Richardson system previously used for tumor grading.

Why Breast Cancer Is Graded

If you've had a breast biopsy and have been diagnosed with breast cancer, you will need to know which treatments are best for you and what your prognosis will be.

To do so, your cancer will need to be staged. Cancer staging is sometimes confused for cancer grading, but they are not the same thing.

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 grading is just one of those factors. It evaluates how the cancer cells look under the microscope (physical characteristics, distribution) to predict how fast a tumor is likely to spread.

Cancer grading is just one of the measures used to stage breast cancer. Others include the size and location of the tumor, the cancer cell type, the number of lymph nodes affected, and the degree of metastasis (spread).

How a Breast Cancer Grade Is Determined

The Nottingham grading system is an update of the previous grading criteria, the Bloom-Richardson system, which was first established in 1957. Nottingham evaluates the cancer cell structure and distribution to determine how aggressive the malignancy will be.

Low-grade tumors, which look more like normal cells, tend to grow slowly, while high-grade tumors are abnormal-looking and spread fast.

There are three factors a pathologist will consider when evaluating tumor cells: tubule formation, miotic rate, and nuclear grade. Each of which is given a score from 1 (most normal) to 3 (least normal).

These values are then added, the total of which will indicate the tumor grade.


Tubule Formation

This refers to how much of the tumor tissue has normal breast (milk) ducts. Possible scores are 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 dividing (mitotic) cells seen under the microscope at 400-times magnification. Scoring is as follows:

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


Nuclear Grade

This is the evaluation of the size and shape of the nucleus in tumor cells. Possible scores include:

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 above three scores are combined to determine the grade of the tumor. Higher grades confer to increased aggressiveness and an increased propensity 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 fast)
8 to 9 Grade 3 tumor Poorly-differentiated (abnormal, growing quickly, aggressive)

Grading and Tumor Staging

The cancer grade will be used to stage your cancer—that is, how advanced your cancer.

The staging will help your doctor decide which treatment can fully eradicate the malignancy with the least amount of harm. For example, early-stage cancer may require surgery or radiation, while advanced-stage cancer may need to be treated with chemotherapy.

Cancer staging can be divided into two distinct methodologies:

  • Clinical staging is based on all of the available information obtained before surgery, including the results of your physical exams and imaging studies (such as X-rays and computed tomography, or CT, scans).
  • Pathologic staging uses the same tests but also includes the pathologist’s evaluation of tumor tissue and lymph nodes removed in surgery.

Pathologic staging is considered to be more accurate because it involves the direct examination of the tumor. With that being said, clinical staging may be appropriate in some situations given that not all cancers require surgery.

TNM Classification

With regards to breast cancer, the TNM Classification of Malignant Tumor (TNM) is the system most commonly used for staging. It is widely used for the staging of many cancers (with the exception of blood cancers or malignancies of the central nervous system). Most common tumors have their own TNM classification system.

TNM stands for tumor, nodes, and metastasis, specifically the size of the tumor (T), the number of lymph nodes affected by cancer (N), and the degree of metastasis (M).

The TNM system can be used for both clinical and pathologic staging as denoted by the use of a lower-case "c" or "p" before the cancer stage (for example, cT3N1M0 or pT2N0).

When a pathology report is received by your doctor, both the cancer grade and stage—on a scale of 0 (non-invasive) to 4 (metastatic)—will be included.

The pathology report will also detail:

  • Whether you have one or more tumors in the affected breast
  • To what extent the malignancy is confined to the breast
  • Whether cancer is found in the lymph nodes under the arm
  • If the cancer has spread to the nipple and skin
  • If there are cancer-free margins around the extracted tumor
  • If the cancer is estrogen-positive or estrogen-negative (an indication of whether the hormone can influence tumor growth)

Based on these findings and features, your doctor will formulate a treatment plan for you to review and discuss. If there is a finding or value you don't understand, ask your doctor about it and how it influences the treatment decision.

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