When prostate cancer is found in a biopsy, it will be graded to estimate
how quickly it is likely to grow and spread. The most commonly
used prostate cancer grading system, called Gleason grading,
evaluates prostate cancer cells on a scale of 1 to 5, based
on their pattern when viewed under a microscope.
Cancer cells that still resemble healthy prostate cells have
uniform patterns with well-defined boundaries and are considered
well-differentiated (Gleason grades 1 and 2). The more closely
the cancer cells resemble prostate tissue, the more the cells
will behave like normal prostate tissue and the less aggressive
the cancer. Gleason grade 3, the most common grade, shows
cells that are moderately differentiated, that is, still somewhat
well-differentiated, but with boundaries that are not as well-defined.
Poorly-differentiated cancer cells have random patterns with
poorly defined boundaries and no longer resemble prostate
tissue (Gleason grades 4 and 5), indicating a more aggressive
cancer.
Schematic
diagram of the Gleason grading system
courtesy of Dr. D.F. Gleason, Minneapolis, Minnesota
Integrated design courtesy of Pittsburgh Supercomputing
Center
Gleason grade versus Gleason score
Prostate cancers often have areas with different grades. A
combined Gleason score is determined by adding the
grades from the two most common cancer cell patterns within
the tumor. For example, if the most common pattern is grade
4 and the second most common pattern is grade 3, then the
combined Gleason score is 4+3=7. If there is only one pattern
within the tumor, the combined Gleason score can be as low
as 1+1=2 or as high as 5+5=10. Combined scores of 2 to 4 are
considered well-differentiated, scores of 5 to 6 are considered
moderately-differentiated and scores of 7 to 10 are considered
poorly-differentiated. Cancers with a high Gleason score are
more likely to have already spread beyond the prostate gland
at the time they were found.
Significance of Gleason score on prognosis
In general, the lower the Gleason score, the less aggressive
the cancer and the better the prognosis (outlook for cure
or long-term survival). The higher the Gleason score, the
more aggressive the cancer and the poorer the prognosis for
long-term, metastasis-free survival.
The Prostate Cancer pages of this Web site are part of the Comprehensive Prostate Cancer Awareness Program (CPCAP), a major regional effort to reduce the rates of death and illness caused by prostate cancer in southwestern Pennsylvania. Funding for CPCAP is provided by a grant from the Commonwealth of Pennsylvania.
