In pathology,<unk> is a measure of the progress of tumors and other neoplasms.  Some pathology<unk> systems apply only to malignant neoplasms (cancer);  others apply also to benign neoplasms.
Pathology<unk> systems are used to classify neoplasms in terms of how abnormal the cells appear microscopically and what may be the outcome in terms of rate of growth, invasiveness, and dissemination. Cancer is a disorder of excessive cell growth, hence cancer cells often are poorly differentiated. The grade reflects the degree of cellular differentiation and refers to how much the tumor cells resemble or differ from the normal cells of the same tissue type.
An important part of evaluating a cancer is to determine its histologic grade.  Grade is a marker of how differentiated a cell is.  Grade is rated numerically (Grade 1-4) or descriptively (e.g., "high grade" or "low grade").  The higher the numeric grade, the more "poorly differentiated" is the cell, and it is called "high grade".  A low grade cancer has a low number and is "well-differentiated."  Grade is most commonly given on a three-tier scale.  A cancer that is very poorly differentiated is called anaplastic.  Tumors may be graded on four-tier, three-tier, or two-tier scales, depending on the institution and the tumor type.
The most commonly used system of<unk> is as per the guidelines of the American Joint Commission on Cancer. As per their standards, the following are the<unk> categories.
GX                Grade cannot be assessed
G1                Well differentiated (Low grade)
G2                Moderately differentiated (Intermediate grade)
G3                Poorly differentiated (High grade)
G4                Undifferentiated (High grade)<unk> systems are also different for each type of cancer.
The Gleason system used to grade the adenocarcinoma cells in prostate cancer is the most famous. This system uses a<unk> score ranging from 2 to 10. Lower Gleason scores describe well-differentiated less aggressive tumours.
Other systems include the Bloom-Richardson system (breast cancer) and the Fuhrman system (kidney cancer).
The tumor grade, along with the staging, is used to develop an individual treatment plan and to predict the patient's prognosis.
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