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Tumor Grade: Questions and Answers 

1. What is a tumor? 

In order to understand tumor grade, it is helpful to know how tumors form. The body is 

made up of many types of cells. Normally, cells grow and divide to produce new cells in 

a controlled and orderly manner. Sometimes, however, new cells continue to be 

produced when they are not needed. As a result, a mass of extra tissue called a tumor 

may develop. A tumor can be benign (not cancerous) or malignant (cancerous). Cells in 

malignant tumors are abnormal and divide without control or order. These cancerous 

cells can invade and damage nearby tissue, and spread to other parts of the body 

(metastasize). 

2. What is tumor grade? 

Tumor grade is a system used to classify cancer cells in terms of how abnormal they look 

under a microscope and how quickly the tumor is likely to grow and spread. Many 

factors are considered when determining tumor grade, including the structure and growth 

pattern of the cells. The specific factors used to determine tumor grade vary with each 

type of cancer. 

Key Points 

• Tumor grade is a system used to classify cancer cells in terms of how 

abnormal they look under a microscope and how quickly the tumor is 

likely to grow and spread (see Question 2). 

• A pathologist (a doctor who identifies diseases by studying cells under a 

microscope) determines whether the tumor is benign or malignant. The 

pathologist also determines the tumor grade (see Question 3). 

• Each type of cancer is graded using a different grading system (see 

Question 5). 

• Doctors consider tumor grade and other factors when developing an 

individual treatment plan for a patient (see Question 6). 
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Histologic grade, also called differentiation, refers to how much the tumor cells resemble 

normal cells of the same tissue type. Nuclear grade refers to the size and shape of the 

nucleus in tumor cells and the percentage of tumor cells that are dividing. 

Tumor grade should not be confused with the stage of a cancer. Cancer stage refers to 

the extent or severity of the cancer, based on factors such as the location of the primary 

tumor, tumor size, number of tumors, and lymph node involvement (spread of cancer into 

lymph nodes). (More information about staging is available in the NCI fact sheet 

Staging: Questions and Answers, which can be found at 

http://www.cancer.gov/cancertopics/factsheet/Detection/staging on the Internet.) 

3. How is tumor grade determined?

If a tumor is suspected to be malignant, a doctor removes a sample of tissue or the entire 

tumor in a procedure called a biopsy. A pathologist (a doctor who identifies diseases by 

studying cells under a microscope) examines the tissue to determine whether the tumor is 

benign or malignant. The pathologist can also determine the tumor grade and identify 

other characteristics of the tumor cells. 

4. What do the different tumor grades signify?

Based on the microscopic appearance of cancer cells, pathologists commonly describe 

tumor grade by four degrees of severity: Grades 1, 2, 3, and 4. The cells of Grade 1 

tumors resemble normal cells, and tend to grow and multiply slowly. Grade 1 tumors are 

generally considered the least aggressive in behavior. 

Conversely, the cells of Grade 3 or Grade 4 tumors do not look like normal cells of the 

same type. Grade 3 and 4 tumors tend to grow rapidly and spread faster than tumors with 

a lower grade. 

The American Joint Commission on Cancer recommends the following guidelines for 

grading tumors (1): 

Grade 

GX Grade cannot be assessed (Undetermined grade) 

G1 Well-differentiated (Low grade) 

G2 Moderately differentiated (Intermediate grade) 

G3 Poorly differentiated (High grade) 

G4 Undifferentiated (High grade) 

5. Does the same grading scale apply to all tumors? 

Grading systems are different for each type of cancer. For example, pathologists use the 

Gleason system to describe the degree of differentiation of prostate cancer cells. The 

Gleason system uses scores ranging from Grade 2 to Grade 10. Lower Gleason scores 
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describe well-differentiated, less aggressive tumors. Higher scores describe poorly 

differentiated, more aggressive tumors. Other grading systems include the 

Bloom-Richardson system for breast cancer and the Fuhrman system for kidney cancer.

6. Does tumor grade affect a patient’s treatment options? 

Doctors use tumor grade and many other factors, such as cancer stage, to develop an 

individual treatment plan for the patient and to predict the patient’s prognosis. Generally, 

a lower grade indicates a better prognosis (the likely outcome or course of a disease; the 

chance of recovery or recurrence). However, the importance of tumor grade in planning 

treatment and estimating a patient’s prognosis is greater for certain types of cancers, such 

as soft tissue sarcoma, primary brain tumors, lymphomas, and breast and prostate cancer. 

Patients should speak with their doctor about tumor grade and how it relates to their 

diagnosis and treatment. 

Selected References 

1. American Joint Committee on Cancer. AJCC Cancer Staging Manual. 6th ed. New 

York, NY: Springer, 2002. 

# # # 

Related Resources

Publications (available at http://cancer.gov/publications)

• National Cancer Institute Fact Sheet 5.32, Staging: Questions and Answers

• National Cancer Institute Fact Sheet 6.7, Cancer: Questions and Answers

• National Cancer Institute Fact Sheet 8.2, Understanding Prognosis and Cancer 

Statistics

• What You Need To Know AboutTM Cancer

National Cancer Institute (NCI) Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 

Online 

NCI’s Web site: http://cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp 

This fact sheet was reviewed on 5/19/04