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Lymphoma and Pets
Tumor grading is fairly uncommon in lymphoma, although it is still sometimes used in the diagnosis of follicular lymphoma.
When a pathologist examines cancerous tissue from a biopsy under a microscope, he or she is looking for differences in microscopic appearance between healthy cells from that tissue and tumor cells from that tissue, and how they both fit in with the surrounding tissue structure. They want to see how the tumor cells compare to healthy cells in their appearance.
The grade of the tumor is determined by how different cancer cells look when compared to normal or healthy cells.
If the tumor cells look fairly similar to healthy cells, the pathologist says the tumor is "well-differentiated." A well-differentiated tumor generally means that the cancer is not aggressive, or indolent.
As an indicator of aggressiveness, a well-differentiated tumor would be a low grade tumor, or grade one (G1).
The next rung on the ladder is a moderately differentiated tumor, which would also be a low-grade tumor but would be tagged as grade two (G2).
On the other hand, if the tumor cells look very different than the healthy cells, he or she says that the tumor is "poorly differentiated."
The less that the cancer cells seem to fit in with the existing tissue, the greater the ability of the cancer to spread. Grade three (G3) and grade four (G4) tumors are high grade tumors, either poorly differentiated, or worse, undifferentiated.
Grade vs. Stage
Grading is not the same thing as staging. A grade measures 'differentiation' and tells you about the relative aggressiveness of the cancer. The stage measures how much or how little the cancer has spread from the site of origin. A person could be diagnosed with a grade two non-Hodgkin's follicular lymphoma, stage III, or a grade three MALT lymphoma, stage II.
It is important to remember that specialists in some subtypes of cancer use their own established grading systems, such as the Nottingham system used in grading breast cancer, that do not apply to lymphomas.
Lymphoma Research Foundation
American Joint Committee on Cancer
National Cancer Institute