By Dr Ananya Mandal, MD
Prostate cancer staging is performed for two main reasons: to guide decisions about the optimal treatment approach and to predict patient outcomes.
There are several staging systems that can be used to classify the different pathological states of prostate cancer. One of the most commonly used systems is the American Joint Committee on Cancer (AJCC) TNM staging system.
According to this system, five main elements are considered. The TNM acronym stands for "T"umor size, "N"ode (lymph node) involvement and "M"etastasis or spread of the tumor to other organs. The other two factors taken into consideration using this staging system are the prostate-specific antigen (PSA) level at diagnosis and the Gleason grade allocated on prostate biopsy.
The extent of a prostate cancer tumor may be categorized into four groups:
The tumor cannot be felt on digital rectal examination (DRE) or seen on imaging studies such as transrectal ultrasound. This category is further divided into T1a where less than 5% of the tissue removed during surgery is cancerous and T1b where more than 5% of the removed tissue is cancerous.
The tumor can be felt on DRE or seen on transrectal ultrasound but still seems to be confined within the prostate gland. Sub-classifications include T2a tumors, where the cancer is in one half or less of only one side of the prostate; T2b where the cancer is in more than half of only one side of the gland and T2c where the cancer is present in both sides of the gland.
The cancer has started to grow and spread beyond the prostate and may involve the seminal vesicles. Further subdivisions include T3a where the cancer has spread beyond the prostate but does not involve the seminal vesicles and T3b where the cancer has spread to the seminal vesicles.
In this stage, the cancer has grown into tissues adjacent to the prostrate, other than the seminal vesicles.
Nearby lymph node involvement may be categorized into the following:
- NX - The spread to nearby lymph nodes is not assessed
- N0 - The cancer has not spread to any of the nearby lymph nodes
- N1 - The cancer has spread to nearby lymph nodes
The degree of cancer spread is classified as follows:
- M0 - The cancer has not spread beyond the nearby lymph nodes
- M1 - The cancer has spread beyond the nearby lymph nodes to:
- lymph nodes outside of the pelvis - M1a
- the bones - M1b
- other organs (with or without spread to the bones) such as the liver, lungs and brain - M1c
Stages of prostate cancer
Once the TNM classification of a prostate cancer has been determined, this information is combined with the Gleason score and PSA level to assign a cancer stage:
- Stage I includes either of the following:
- T1, N0, M0 as well as a Gleason score of 6 or less and PSA less than 10
- T2a, N0, M0 and Gleason score 6 or less, PSA less than 10
- Stage IIA includes any one of the following:
- T1, N0, M0 and Gleason score of 7, PSA less than 20
- T1, N0, M0 and Gleason score of 6 or less and PSA between 10 and 20
- T2a or T2b, N0, M0 and Gleason score of 7 or less and PSA less than 20
- Stage IIB includes any one of the following:
- T2c, N0, M0, any Gleason score and any PSA
- T1 or T2, N0, M0, any Gleason score and PSA over 20
- T1 or T2, N0, M0, Gleason score of 8 or higher and any PSA
- Stage III
- T3, N0, M0, any Gleason score and any PSA
- Stage IV includes any one of the following:
- T4, N0, M0, any Gleason score and any PSA
- Any T, N1, M0, any Gleason score and any PSA
- Any T, any N, M1, any Gleason score and any PSA
Reviewed by Sally Robertson, BSc