Why do doctors grade tumors?
Cancer is second only to heart disease as a cause of death in the United States. While cancer has many different forms, cancer generally is characterized by a large population of deviant cells that divide without limit. These cells collectively form a "malignant tumor" (as opposed to a "benign tumor", which is not cancerous). As a malignant tumor grows and spreads, it increasingly hinders normal body functions and threatens the well-being of its victim. One key to treating cancer is being able to predict the likelihood and rate at which a tumor will grow and infiltrate the body. Assigning the tumor a grade according to an accepted tumor grading system is one of the approaches that pathologists take in making this prediction.
How are tumors graded?
The first step in grading a tumor is to perform a biopsy, which entails removing a portion of the tumor from the patient. Cells from the removed mass are then viewed by microscope and it is determined at that time whether the tumor is benign or malignant. If the tumor is found to be malignant, the pathologist visually inspects the cells to determine the degree to which they resemble cells from normal tissue that is adjacent to the tumor, and assigns a grade based on this inspection. The more the tumor cells resemble the surrounding normal cells, the lower the grade.
What specifically are the different grades that are assigned and what do the mean?
The American Joint Committee on Cancer recommends that a tumor be assigned one of five tumor grades: G1, G2, G3, G4 or GX. A G1 grade is the most favorable to the patient and this grade is assigned when it is determined that the tumor cells are very much like the surrounding normal cells, whereas a G4 grade, which is least favorable to the patient, means that the tumor cells are very much unlike the surrounding normal cells. G1 grade tumors are expected to grow and spread very slowly, while G4 grade tumors are expected to grow and spread quickly. G2 and G3 grade tumors lie in between G1 and G4 tumors with respect to their appearance to normal surrounding cells and their expected growth and spread rate. A GX grade simply means that a grade has not or cannot be determined.
Do tumor grades influence treatment selection?
Doctors do use tumor grades as a factor in assessing treatment options. G4 tumors typically are treated more aggressively than are G1 tumors. However, it is important to understand that tumor grade is merely one factor that is used in selecting a course of treatment. Another important factor, for example, is the stage that the cancer has reached. Cancer stage is distinct from tumor grade in that cancer stage refers to how much the cancer has actually spread (as opposed to how quickly it is expected to spread, which is what the tumor grade signifies).
Are all forms of cancerous tumors graded according to the American Joint Committee on Cancer’s recommended system?
Not all forms of cancerous tumors are graded exactly according to the American Joint Committee on Cancer’s recommended system. That particular system is merely one recommended system and while most cancerous tumors are in fact graded according to that method, others are graded by using similar but somewhat distinct approaches. Notable among these are the grading systems for prostate, kidney and breast cancer tumors. (For example, prostate cancer is graded on a 2-to-10 scale, with 2 being assigned to those prostate tumors that are likely to grow and spread the slowest and 10 being assigned to those prostate tumors that are likely to grow and spread the fastest.)
For more information on tumor grading and how it affects treatment selection, please consult your doctor. This article is meant only to provide basic information on this topic and is in no way meant to replace your doctor’s own opinion.
American Joint Committee on Cancer. AJCC Cancer Staging Manual. 6th ed. New York, NY: Springer, 2002.
Cancer In-Depth, Mayo Clinic: https://www.mayoclinic.com/health/cancer/DS01076/tab=InDepth
Leading Causes of Death, Center for Disease Control and Prevention: https://www.cdc.gov/nchs/fastats/lcod.htm
Tumor Grade Questions and Answers, National Cancer Institute: https://www.cancer.gov/cancertopics/factsheet/Detection/tumor-grade