Prostate cancer: How do doctors estimate how it will progress?

Photo of three older men talking (PantherMedia / Diego Cervo) Whether and how prostate cancer continues to grow will vary from person to person: Some tumors are small and grow either slowly or not at all. Others are large and grow rapidly. Various examinations can be used to predict which group the cancer is in.

When choosing a treatment, it's important to know how the cancer will probably progress. The treatment options that are considered depend on

  • how big the tumor is (stage), and
  • the likelihood that it will grow (risk of progression).

Various examinations can be used to determine the tumor stage and risk of progression. They include the following:

  • Feeling the prostate (palpation)
  • Imaging techniques (ultrasound and MRI)
  • A blood test to determine the prostate-specific antigen level (PSA level)
  • Tissue sample ("punch" biopsy)

If the cancer is at an advanced stage, further imaging techniques (e.g. computed tomography, or CT) can be used in order to see whether it has led to tumors (metastases) in other parts of the body. The following information is about localized prostate cancer. That means that the cancer has not spread to the lymph nodes and has not yet led to any metastases.

How is the tumor stage determined?

The tumor stage describes how big the tumor is and whether it has already spread. It is notated based on a system called the TNM classification:

  • T describes how much the tumor has spread
  • N shows whether the lymph nodes are affected
  • M indicates whether metastases have formed

The following table shows the tumor stages.

Table: Information used in the TNM staging system for prostate cancer, and what the categories mean
Factor Category Subcategory
Original tumor (primary tumor)

T1:

No tumor can be found using palpation (feeling with a finger) or ultrasound exams

T1a:

Found by chance, less than 5% of the tissue contains cancer cells

T1b:

Found by chance, more than 5% of the tissue contains cancer cells

T1c:

After high PSA levels were measured, cancer cells were found in tissue samples (a biopsy)

 

T2:

The tumor can be felt with a finger or seen in an ultrasound, but has not yet spread to other parts of the body

T2a:

The tumor is in less than one half of only one side (left or right) of the prostate

T2b:

The tumor is in more than half of one side (left or right) of the prostate

T2c:

The tumor is in both sides of the prostate

 

T3:

The tumor has spread outside the prostate into the connective tissue around the prostate or the seminal vesicles

 
 

T4:

The tumor has spread further, to nearby organs such as the bladder or bowel

 
Lymph nodes

N0:

There are no tumors in nearby lymph nodes

N1:

Nearby lymph nodes have cancer in them

 
Metastases

M0:

No metastatic tumors were found

M1:

Metastatic tumors were found

 

Localized prostate cancer includes tumors in categories T1 and T2 that have not spread to the lymph nodes (N0) and have not formed metastases (M0). So, for instance, T2a N0 M0 would be one possible TNM classification for a particular case of localized prostate cancer.

How is the risk of progression determined?

Localized prostate cancer tumors are divided into various risk groups (risk of progression) according to whether and how they are likely to progress. The following information is needed in order to determine the risk of progression:

  • The exact tumor stage (TNM)
  • The PSA levels
  • The Gleason score

The Gleason score is determined based on what the tissue samples look like under the microscope. It describes how much the prostate cells have changed. The lowest score for prostate cancer is 6 and the highest is 10. Tumors with a lower score grow more slowly than tumors with a higher score. To determine the Gleason score, the two tissue samples with cells that have changed the most are given a Gleason grade describing how aggressive the tumor cells are. Those two grades are then added together. For instance, if the first sample has a Gleason grade of 4 and the second sample has a Gleason grade of 3, the Gleason score is 7.

The cancer is assigned to one of four groups, based on the tumor stage, the PSA level and the Gleason score:

  • Very low risk
  • Low risk
  • Intermediate risk
  • High risk

Very low-risk prostate cancer and low-risk prostate cancer are often grouped together and described as "low-risk" prostate cancer.

The following table shows the criteria used for the four risk groups and the usual treatment options for each group:

Table: Risk groups for localized prostate cancer
Risk Criteria Treatment options
Very low risk
  • Tumor stage: up to T2a and
  • PSA level: up to 10 nanograms per milliliter (ng/ml) and
  • Gleason score: 6

Additionally:

  • Number of affected tissue samples: No more than two of the 10 to 12 tissue samples have cancer cells in them.
  • Proportion of tumor cells in the abnormal tissue samples: In those one or two abnormal tissue samples, less than 50% of the tissue is made up of cancer cells.
  • Active surveillance
  • External radiotherapy
  • Internal radiotherapy (brachytherapy)
  • Surgery to remove the prostate
Low risk
  • Tumor stage: up to T2a and
  • PSA level: up to 10 ng/ml and
  • Gleason score: 6
  • Active surveillance
  • External radiotherapy
  • Internal radiotherapy (brachytherapy)
  • Surgery to remove the prostate
Intermediate risk

At least one of these criteria applies:

  • Tumor stage: T2b or
  • PSA level: between 10 and 20 ng/ml or
  • Gleason score: 7
  • External radiotherapy
  • Combination of internal and external radiotherapy
  • Surgery to remove the prostate
High risk

At least one of these criteria applies:

  • Tumor stage: T2c or
  • PSA level: more than 20 ng/ml or
  • Gleason score: 8 or more
  • External radiotherapy
  • Combination of internal and external radiotherapy
  • Surgery to remove the prostate