Staging and Grading

Doctors are continually searching for methods to determine how aggressive a given prostate cancer is in an individual patient so they can choose the best treatments. As an aid, experts have devised different classification systems that help assess the properties of the cancer. These systems include staging and grading the tumors and measuring PSA levels. In general, the higher the stage, grade, and PSA numbers, the more severe the condition and the more aggressive the treatment. Current classifications systems have significant limitations in guiding treatment choices. Newer tests, markers, and imaging techniques may eventually improve the accuracy of staging categories.

Staging Systems

A tumor's stage is an indication of how far it has spread from its original site. Cancers are staged according to whether they are still localized (still within the prostate gland) or have spread beyond the original site. Two prostate cancer staging systems are commonly used: the TNM system and the Jewett system. To avoid confusion, this report only uses the TNM system. The TNM system is explained in detail, and the Jewett system is explained in reference to the TNM system.

TNM Staging System

The TNM system refers to clinical tumor stages as:

T for tumor.

N for regional lymph nodes.

M for metastasis (tumors developing outside the prostate).

T Stages

T followed by numbers 0 through 4 refers to the size and extent of the tumor itself.

Stage

Description

T1

The tumor cannot be felt or seen using imaging techniques.

T1a. Cancer cells are incidentally found in 5% or less of tissue samples from prostate surgery unrelated to cancer.

T1b. Cancer cells found in more than 5% of samples.

T1c. Cancer cells identified by needle biopsy, which is performed because of high PSA levels.

T2

The cancer is confined to the prostate but can be felt as a small well-defined nodule.

T2a. Tumors are in half a prostate lobe.

T2b. Tumors are in more than half a lobe.

T2c. Tumors in both lobes.

T3

The tumor extends through the prostate capsule.

T4

The tumor is fixed to or invades adjacent structures.

N Stages

N followed by 0 to 3 refers to whether the cancer has reached the regional lymph nodes, which are located next to the prostate in the pelvic region.

Stage

Description

N0

Regional lymph nodes are still cancer-free.

N1

A small tumor is in a single pelvic node.

N2

A medium-size tumor is in one node or small tumors are in several nodes.

N3

A large tumor is in one or more nodes.

M Stages

M stages refer to metastasis (tumors developing outside the prostate).

Stage

Description

M0

Metastasis has not occurred (cancer has not spread beyond the regional lymph nodes).

M1a

Cancer has spread to lymph nodes beyond the regional lymph nodes.

M1b

Cancer has invaded the bones.

M1c

Cancer has spread to other sites.

Jewett Staging System

The stages in the Jewett system are roughly equivalent to the stages in the TNM system as follows:

Jewett Stage

TNM Stages

A

T1

B

T2

C

T3, T4

D

N1, N2, N3, M1

The Gleason Grading System

Tumors are assigned scores according to a scale known as the Gleason system, which measure how well or how poorly organized they are under the microscope. The first step is to grade the tumors:

  • Grade 1: Single, well-packed tumors
  • Grade 2: Single, more loosely arranged and less uniform tumors
  • Grade 3: Single tumors of different sizes and patterns, with cellular breakdown becoming increasingly worse
  • Grade 4: Irregular tumor masses, fused together; may show clear cells
  • Grade 5: The tumors have broken down and cellular structure has markedly deteriorated

Two-thirds of prostate cancers have a mix of tumor grades. To determine a prognosis, two numbers are assigned, representing the dominant grade and then the minor grade. The cancer is then "scored" by adding the dominant grade plus the minor grade. For example, a tumor with a dominant grade of 3 and a minor grade of 4 are given a Gleason score of 7. The following scores are often used to suggest how well or poorly the tumor is differentiated. The higher the score, the more severe the break-down of their cellular structure and the more likely they are to spread aggressively:

  • Score 2-4: Well-differentiated. Indicates about a 95% chance for surviving 15 years without aggressive treatment.
  • Score 5-6: Moderately well differentiated. Slightly lower chance of survival that decreases with time.
  • Score 7-10: Moderately poorly to poorly differentiated, with 15-year survival rates of 15 - 40%.