Grading of tumors
Grading of tumors is a crucial classification system used to evaluate malignant tumors based on how much their cells differ from normal tissue cells, as observed under a microscope. This process is conducted by specialized medical doctors known as pathologists, who analyze tissue samples obtained through procedures such as biopsies or tissue scraping. The grading system not only assesses the tumor's cellular characteristics but also its potential aggressiveness in terms of growth and metastasis, which is the spread of cancer to other organs.
Tumor grades provide vital information for healthcare providers in developing effective treatment plans, with higher-grade tumors typically indicating a need for more aggressive intervention. Two key aspects of tumor grading are histologic grade and nuclear grade, which examine the resemblance of cancer cells to normal tissue and the characteristics of the cell nuclei, respectively. The American Joint Commission on Cancer has established a grading scale that ranges from Grade 1 (low grade) to Grade 4 (high grade), with variations specific to different cancer types, such as the Gleason scale for prostate cancer.
It is important to note that the accuracy of tumor grading can significantly depend on the experience of the pathologist, as each cancer type has distinct cellular traits. Overall, understanding tumor grading is essential for assessing prognosis and potential treatment outcomes for patients diagnosed with cancer.
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Grading of tumors
DEFINITION: The grading of tumors is a system devised to classify malignant tumors. The grade is determined by how aberrant (different from what is expected) the tumor cells are in relation to normal tissue cells when viewed under a microscope. The grading of tumor cells is performed by a medical doctor who specializes in pathology. This system also considers how aggressive the tumor is in regard to growth and metastases (the spread of cancer cells to other organs).
Cancers diagnosed: All
Why performed: Tumors are graded so that physicians have information about the tumor to use in developing a treatment plan for the patient. The higher the grade of the tumor, the more aggressively it is treated. A tumor grade can also give an indication of the likelihood that the cancer can be cured, as well as of the prognosis of the patient.
Patient preparation: Tumor grade is determined by analysis of tissue cells from the tumor. The patient is not directly involved with the grading of the tumor, which is performed by a pathologist.
Steps of the procedure: Specimens (small samples) to be used for grading a tumor are extracted through biopsy (removal of tissue from a tumor) or tissue scraping. An example of a tissue scraping procedure is the Papanicolaou smear (Pap smear), in which cells are scraped from the cervix of the uterus. The tissue samples are then placed in a container with a preservative solution, such as formaldehyde. The pathologist takes thin slices of tumor tissue and prepares slides for viewing under a microscope. Then the slides are examined as to cell structure and growth pattern. Each type of cancer has its own characteristics, although there is a similarity between cells of tumors from similar types of tissue. For example, all sarcomas (cancer of the muscle) are similar no matter the muscle in which they are discovered.
Two important factors identified by the pathologist are histologic grade and nuclear grade. Histologic grade refers to the amount of differentiation between the tumor cells and the cells of the tissue where the tumor resides. Cancer cells that appear quite similar to the tissue cells are low grade, whereas cancer cells that are large and oddly shaped, bearing little resemblance to normal cells, are considered higher grade. Nuclear grade considers the size, shape, and activity of the nucleus of each cancer cell. Nuclei that resemble closely those of normal cells are low grade. Nuclei that are large and oddly shaped, bearing little resemblance to normal nuclei, are higher grade. Nuclear grade also considers the relative number of cancer cells that are dividing, as evidenced by the signs of cell mitosis (cell division). In cell mitosis, it is possible to see the genetic material of the cells duplicating and splitting into two cells.
After the procedure: After examining the cancer cells, the pathologist writes a report that describes what the tumor cells look like and the pathologist’s impression as to the type and grade of the tumor. Commonly used terms are metaplasia, hyperplasia, and atypical hyperplasia. Metaplasia of cells describes the reversible transformation of normal cells to a slightly different form by injury or stress. It is thought that metaplasia could lead to cancer. Hyperplasia of cells indicates that the cells are reproducing at an abnormally high rate. Atypical hyperplasia signifies that, in addition to the fact that cells are reproducing at a high rate, there are also cells that appear different from normal cells.
Risks: The risk for the grading of tumors is if the pathologist is incorrect in their judgment of the tumor cells. The more experience a pathologist has with a type of tumor cell, the more accurate their assessment will likely be. As a result, pathologists often specialize in certain types of tumors.
Results: The American Joint Commission on Cancer (AJCC) has developed generic (basic) guidelines for the grading of tumors. They are as follows:
- Grade X: tumor cell grade cannot be assessed
- Grade 1: tumor cells appear quite similar to normal cells (low grade)
- Grade 2: moderate differences exist between the tumor cells and normal cells (intermediate grade)
- Grade 3: substantial differences exist between the tumor cells and normal cells (high grade)
- Grade 4: tumor cells bear little or no resemblance to normal cells (high grade)
In practice, variations of this generic tumor grading scale are used. A tumor grading scale has been developed for each type of cancer. For example, prostate cancer is graded by the Gleason scale, which includes grades 2 through 10.
Bibliography
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Damjanov, Ivan, and Fang Fan, eds. Cancer Grading Manual. 2nd ed. New York: Springer, 2013. Print.
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