Tumor grading is an estimate of the tumor's malignancy and aggressiveness based on how the tumor cells appear under a microscope and the number of malignant characteristics they possess.
Tumor grading, together with the stage of the tumor, assists doctors in planning treatment strategies. Although grading is an important part of describing most cancers, it is extremely important in helping to determine the course of treatment for specific cancers such as soft tissue sarcomas , brain tumors, lymphomas, breast and prostate cancer . Generally higher grade and higher stage tumors require more drastic therapy than lower grade and stage tumors. Tumor grade and stage also help doctors give an estimation of the prognosis of the patient. Patients with lower grade and stage tumors usually have a more positive prognosis than patients with higher grade and stage tumors. Patients should thoroughly discuss the grade and stage of their tumor with their physician, asking about necessary treatments and prognosis.
Before a tumor can be assigned a grade, a sample of tissue must be removed for microscopic evaluation. Tissue samples can be obtained through one of various types of biopsy or through exfoliative cytology (e.g. Pap smear). A pathologist analyzes various characteristics of the tissue. Some characteristics include the size and shape of the nucleus; the ratio of the volume of the nucleus to the volume of the cytoplasm; the relative number of dividing cells called the mitotic index; the organization of the tissue; the boundary of the tumor; and how well differentiated the cells appear—how close to normal the cells seem in maturityu and function.
Benign tumors have normal looking cells. That is, they have small and regular-shaped nuclei, small nuclear volume relative to the rest of the cellular volume, a relatively low number of dividing cells, normal and well-differentiated tissue that has a well defined tumor boundary. However, malignant tumors generally have all or several of the following characteristics: large and pleomorphic (irregular-shaped) nuclei, large nuclear volume compared to the rest of the cellular volume, a high number of dividing cells, disorganized and anaplastic (poorly differentiated) tissue that has a poorly defined tumor boundary.
Depending on the number of malignant characteristics present, the American Joint Commission on Cancer has recommended that the tumor be given a grade using G0 through G4.
- G1 Well differentiated (Low-grade and less aggressive)
- G2 Moderately well differentiated (Intermediate-grade and moderately aggressive)
- G3 Poorly differentiated (High-grade and moderately aggressive)
- G4 Undifferentiated (High-grade and aggressive)
Alternatively, Roman numerals I through IV may be used. Low-grade tumors are assigned lower Roman numerals (e.g. grade I), indicating that the tumor is less aggressive. High-grade tumors are assigned higher Roman numerals (e.g. grade IV), indicating that the tumor is very aggressive, growing and spreading quickly.
- I Well differentiated (Low-grade and less aggressive)
- II Moderately well differentiated (Intermediate-grade and moderately aggressive)
- III Poorly differentiated (High-grade and moderately aggressive)
- IV Undifferentiated (High-grade and aggressive)
There are some cancers that have their own grading convention. For example, the Gleason system is a unique grading system that was developed to describe adenocarcinoma of the prostate. Pathologists analyze prostate tissue and give a Gleason score ranging from 2 to 10, subject to the number of malignant characteristics observed. Well differentiated, less aggressive prostate tumors with only a few malignant characteristics are given lower Gleason numbers, while inadequately differentiated, more aggressive prostate tumors that possess many malignant characteristics are assigned higher Gleason numbers.
See Also Tumor staging
Bast, Robert C. Cancer Medicine. B.C. Decker Inc., 2000.
DeVita, Vincent T. Cancer Principles and Practice of Oncolo gy, 5th Edition, Vol. 1 and 2. Lippincott-Raven Publishers, 1997.
Sally C. McFarlane-Parrott
—Poorly differentiated; immature and abnormal in function.
—A non-cancerous tumor that is incapable of invading surrounding tissue and spreading to other areas of the body.
—Description of the similarity of function and appearance of cancer cells when compared to the normal, healthy tissue.
—Evaluating cells that are shed from the body's surface.
—A tumor that is capable of invading surrounding tissue and spreading to other areas of the body.
—Analysis of cells found in vaginal secretions to determine the presence of uterine cancer. Also called Pap test.
—A doctor that examines cells under a microscope to determine the presence of the disease.
—An objective measurement gauging the cancer's progression. Different cancers have different staging systems.
QUESTIONS TO ASK THE DOCTOR
- What are the microscopic characteristics this cancer presents?
- What grade is this cancer?
- What courses of treatment do you recommend for this grade of this type of cancer?