What is a tumor?
In order to understand tumor grade, it is helpful to know how tumors form.
The body is made up of many types of cells. Normally, cells grow and divide to
produce new cells in a controlled and orderly manner. Sometimes, however, new
cells continue to be produced when they are not needed. As a result, a mass of
extra tissue called a tumor may develop. A tumor can be benign (not cancerous)
or malignant (cancerous). Cells in malignant tumors are abnormal and divide
without control or order. These cancerous cells can invade and damage nearby
tissue, and spread to other parts of the body (metastasize).
What is tumor grade?
Tumor grade is a system used to classify cancer cells in terms of how
abnormal they look under a microscope and how quickly the tumor is likely to
grow and spread. Many factors are considered when determining tumor grade,
including the structure and growth pattern of the cells. The specific factors
used to determine tumor grade vary with each type of cancer.
Histologic grade, also called differentiation, refers to how much the tumor
cells resemble normal cells of the same tissue type. Nuclear grade refers to the
size and shape of the nucleus in tumor cells and the percentage of tumor cells
that are dividing.
Tumor grade should not be confused with the stage of a cancer. Cancer stage
refers to the extent or severity of the cancer, based on factors such as the
location of the primary tumor, tumor size, number of tumors, and lymph node
involvement (spread of cancer into lymph nodes). (More information about staging
is available in the NCI fact sheet Staging: Questions and Answers, which can be
found at http://www.cancer.gov/cancertopics/factsheet/Detection/staging on the
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Tumor Grade - Biopsy
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