In pathology, grading is a measure of the progress of tumors and other neoplasms. Some pathology grading systems apply only to malignant neoplasms (cancer); others apply also to benign neoplasms.
Pathology grading 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., "low grade" or "high 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 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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The most commonly used system of grading is as per the guidelines of the American Joint Commission on Cancer. As per their standards, the following are the grading categories.
Grading systems are also different for each type of cancer.
The Gleason system[1], named after Donald Floyd Gleason, used to grade the adenocarcinoma cells in prostate cancer is the most famous. This system uses a grading score ranging from 2 to 10. Lower Gleason scores describe well-differentiated less aggressive tumors. Other systems include the Bloom-Richardson system (breast cancer) and the Fuhrman system (kidney cancer).
| Grade 1 | Low grade | Well-differentiated |
| Grade 2 | Intermediate grade | Moderately-differentiated |
| Grade 3 | High grade | Poorly-differentiated |
| Grade 4 | Anaplastic | Anaplastic |
| Grade 1 | Low grade | Well-differentiated |
| Grade 2 | Intermediate grade | |
| Grade 3 | High grade | Poorly-differentiated |
| Grade 1 | Low grade | Well-differentiated |
| Grade 2 | High grade | Poorly-differentiated |
Experimental cancer studies involve the implantation of tumors subcutaneously in mice. Such studies require a simple mechanism by which to evaluate tumor burden. One such method is to approximate the tumor shape by a spheroid. Two researchers blindly measure tumor length L and width W in millimeters with calipers. The depth is not measured and is assumed to equal the width W. The tumor's volume in cubic millimeters is then approximately 0.52W2L.[2]
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   | National Cancer Institute - Tumor Grade: Q&A - National Cancer Institute |
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