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A cancer cell’s ability to mimic a normal prostate gland cell is called
differentiation. Cancers that look similar to normal tissue are “well
differentiated,” while those appearing very different are “poorly
differentiated.” Cancers in between these two are “moderately differentiated.”
The Gleason system uses this information to grade tumors, indicating how fast
the cancer is growing. A pathologist assigns a Gleason grade ranging from 1
through 5 based on the level of differentiation. The more dissimilar cancer
cells appear from normal prostate tissue and the more they seem to have spread
haphazardly throughout the prostate, the higher the Gleason grade assigned.
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Gleason Grades 1 and 2. Cancer cells closely resemble normal prostate
tissue and are well differentiated. Cancer cells will probably have a
biological behavior relatively close to normal and may not be aggressively
malignant. |
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Gleason Grade 3. The most common grade assigned. These cancer cells are
moderately well differentiated. |
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Gleason Grade 4. May indicate development of a more advanced tumor. This
grade indicates the first main disruption and loss of normal prostate gland
tissue architecture. This is the main class of poorly differentiated prostate
cancer, and its distinction from Grade 3 is the most important decision made by
a pathologist. |
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Gleason Grade 5. The cells do not resemble normal prostate cancer tissue
and do not look different from undifferentiated cancers that might occur in
other parts of the body. This grade is generally associated with a poor
prognosis. It is less common than Grade 4 and seldom seen in men with an early
prostate cancer diagnosis. |
When examining the specimen, a pathologist also tries to identify two
architectural patterns and assigns a grade to each one. There may be a primary
-- or most common pattern -- as well as a secondary pattern, or there only may
be a single, pure grade. Added together, the two numbers create the Gleason
score, also called a Gleason sum, which quantifies how aggressive the cancer
appears. The Gleason score ranges between 2 and 10, with 2 being the slowest
growing cancer and 10 the most aggressive. Most localized prostate cancers are
in the intermediate score range of 5 to 6.
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