The TNM system sets the standards for staging prostate cancer. This aids in decisions regarding treatment. The classifications range from T1-T4, plus the "N" and "M" numbers. Each group is broken down into further categories.

If you see a "T0" on your chart, go about your business - that means no cancer cells are showing. However, we're going to tackle the classifications that are of concern when prostate cancer is indeed present.

The "T" part of the TNM system is designed to determine if cancer cells are contained or they have spread - and to what extent.

T1 - Tumor cannot be detected during a digital rectal exam (DRE) or by ultrasound.

-T1a or T1b - This stage is commonly attributed following a resection of the prostate to improve urine flow. The procedure, called TURP, stands for "transurethral urethral resection of the prostate." A T1a means fewer than 5% cancerous cells were found; T1b, means greater than 5% were identified.

-T1c indicates that these cells were identified following a biopsy.

T2 - At this stage, the tumor has been felt during the DRE, but cancer is confined to the gland.

-T2a - Suspicious areas are confined to 50% or less of one lobe in the gland.
-T2b - Tumor may be present in more than 50% of one lobe.
-T2c - Both lobes are involved.

T3 - Cancer tumor or cells have escaped or broken through the capsule, but no further involvement of other tissue is indicated.

-T3a - Tumor has extended outward from the gland in one spot.
-T3b - Tumor may be breaking through capsule in several locations.
-T3c - Tumor is probably present in one or more seminal vesicles. These are located above the prostate gland, toward the back between the bladder and the large colon.

T4 - Tumor has spread outside the gland and into nearby structures, and beyond the seminal vesicles.

-T4a - Presumably, prostate cancer cells may be found in the bladder neck, the external sphincter, and the rectal area.
-T4b - Indicates invasion of the pelvic wall and levator muscles (basically the pelvic floor).

"N" Classification

This letter refers to lymph node involvement. An N0 means no spread in this areas.

-N1 - Cells have been identified in one node, but the aggregation is less than 2 centimeters at largest point.
-N2 - Involvement in one node, but aggregate of 2-5 centimeters at largest point.
-N3 - Node consumption is greater than 5 centimeters.

"M" Classification

This letter refers to "metastasis," meaning other parts of the body are involved. Again, a "zero" rating indicates no further involvement.

M1a - Cells detected in distant nodes and not including the lymph nodes near the prostate gland.
M1b - Bone involvement.
-M1b(a) - Axial skeleton is affected (but not the appendages - legs, arms).
-M1b(b) - Skeletal plus appendages.
M1c - Prostate cancer cells identified in other organs.

A further level may also be attributed, which is referred to as "G" grading.

When aggressive cell growth is identified, the G rating means the cells themselves are studied and compared to normal cells. Sometimes called a "histologic" reading.

GX - no assessment can be made.
G1 - Noted as similar to normal structuring, but can be differentiated from the normal cells.
G2 - A noticeable difference from normal cells.
G3 - A significant difference from normal cells.

The "G" classification may be combined with the Gleason scoring to make a determination on projected rate of cancer growth in the prostate gland.

The only way to reach a specific determination is for a pathologist to examine the prostate gland following surgical removal. At this point, the Gleason score may go down and in some cases it will go up, even significantly.

Now you have a basic understanding of grading and rating, but there's much more to learn about prostate cancer and treatment decisions.