Tumor Grading

Tumor grading 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.

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 whether the cancer has spread into lymph nodes.

How tumor grade is 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 then 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.

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 cannot be assessed (Undetermined grade)
    Well-differentiated (Low grade)
    Moderately differentiated (Intermediate grade)
    Poorly differentiated (High grade)
    Undifferentiated (High grade)

Grading systems differ 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 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.

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. 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.

This article was posted on August 21, 2005.

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