Here's what I posted earlier. Maybe more than your are looking for, but it really explained GS for me.
The Gleason Scale:
If your diagnostic tests and other examinations reveal a malignant tumor of the prostate, your physician may use the Gleason grading system to help describe the appearance of the cancerous prostate tissue.
In order to do this, a pathologist will look at the biopsied tissue under a microscope. He or she will examine the way that the cancerous cells look compared to normal prostate cells.
If the cancerous cells appear to resemble the normal prostate tissue very closely, they are said to be very well differentiated and are considered Gleason grade 1. This means that the tumor is not expected to be fast growing.
On the other hand, if the cells in question look fairly irregular and very different from the normal prostate cells, then they are very poorly differentiated and are assigned a Gleason grade 5.
Grades 2-4 are used for tumors that fall between grades 1 and 5, with higher numbers corresponding to faster-growing tumors.
Because prostate cancer tissue is often made up of areas that have different grades, the pathologist will closely examine the areas that make up the largest portion of the tissue.
Gleason grades are then given to the two most
commonly occurring patterns of cells.
Once the 2 scores have been assigned, a Gleason score can be determined by adding together the two Gleason grades.
The Gleason score that results will be a number
from 2 to 10. Scores on the higher end of the Gleason grading systen (7 through 10) usually indicate a more serious prognosis.
What is staging in prostate cancer?
To detect and diagnose prostate cancer and to determine the size and extent of the spread- or stage- of the disease, your doctor may perform tests that involve feeling the prostate (DRE), looking at internal parts of the body (scans), measuring the levels of substances in the blood (PSA test), and examining the samples of prostate tissue (biopsy).
Only by knowing how the cancer is growing and exactly where it is located in the body can you and your doctor choose the best treatment for you.
There are 2 systems used to stage prostate cancer:
The most common method of staging prostate cancer is by using a system called the TNM staging system, which stands for Tumor, Node, Metastases.
In addition, the equivalent stages in the A,B,C,D ststem or Whitmore-Jewett staging system are given in Parentheses in the table.
When talking with your doctor, you will frequently hear the following terms regarding the stages of prostate cancer: localized, locally advanced, and metastatic.
Localized prostate cancer is a cancer that is contained within the prostate gland. Locally advanced prostate cancer is a cancer that has spread beyond the prostate to surrounding tissue and may also have spread to the pelvic lymph nodes. Metastatic prostate cancer is a cancer that has spread beyond the prostate and pelvic lymph nodes into other distant parts of the body, such as the bones.
TNM Staging System
T refers to the size of the primary tumor.
N describes the extent of regional lymph node involvement
M refers to the presence or absence of metastates
T STAGING (tumor size):
Stage TX, TO, T1
TX Primary tumor cannot be assessed
TO No evidence of primary tumor
T1 (A) Tumor not clinically apparent
T1a (A1) Tumor incidentally found in <5% of prostate sample
T1b (A2) Tumor incidentally found in >5% of prostate sample
T1c Tumor identified at needle biopsy performed to
investigate PSA elevation
T2 (B) Palpable tumor confined to prostate
T2a (B1N) Tumor involves less than half of one prostate lobe
T2b (B1) Tumor involves more than half of one lobe but not both lobes
T2c (B2) Tumor involves both prostate lobes
T3 (C1-tumor < 6cm) Tumor palpable and extends beyond prostate capsule
T3a (C1) Tumor extends beyond prostate capsule, either on one side (unilaterally) or both sides (bilaterally)
T3b (C1) Tumor invades seminal vesicles
T4 (C2-tumor > 6cm) Tumor is fixed or invades adjacent anatomy other than seminal vesicles:
bladder neck, external sphincter, rectum, levator muscles, and/or pelvic wall
N STAGING (lymph nodes):
Stage NX, NO, N1
NX Regional lymph nodes cannot be assessed
NO No regional lymph node metastasis
N1 (D1) Metastasis in regional lymph node or nodes
M STAGING (metastasis):
Stage MX, MO, M1
MX Presence of distant metastasis cannot be asessed
MO No distant metastasis
M1 (D2) Distant metastasis
M1a (D2) Metastasis to nonregional lymph nodes
M1b (D2) Metastatis to bone
M1c (D2) Metastasis to other distant sites
Detailed information can be found here: