Understanding Prostate Cancer Staging and Grading

A prostate cancer diagnosis sparks many questions. Has the cancer been caught early? How extensive is it? Has it spread to other parts of the body? Not knowing the answers to these questions can be a source of stress and anxiety. Two processes—cancer staging and cancer grading—help provide answers.

“Staging refers to how much the cancer has grown. Is it confined locally within the prostate? Has it spread beyond the prostate and into the lymph nodes, or has the cancer metastasized to the bones? These are the questions staging addresses,” says Rich Bevan-Thomas, M.D., medical director of USMD Prostate cancer. “Grading cancer is different. Grade refers to how the cancer looks under a microscope. The most common type of prostate cancer is adenocarcinoma, which is given a Gleason grade according to how aggressive the cells look. Think of a cancer cell as an egg. The more cracks in the egg, the higher its Gleason grade and the more aggressive the cancer is likely to be.”

Staging and grading take place after a biopsy has been performed to obtain tissue samples from the prostate. During the minimally invasive out-patient procedure, a surgeon uses guided imagery and a fine needle to collect 12 to 24 tissue samples from specific zones of the prostate—along with any suspicious areas that may be visible around the prostate.

These tissue samples are sent to a pathologist for evaluation. If abnormal-looking cancer cells are found, the pathologist ranks them according to the degree of visible change. While early-stage or low-grade cancer cells may look only slightly different than healthy cells, high-grade cancer cells look dramatically different than healthy cells. Think about the cracked egg analogy again.

Each of the tissue samples collected for the biopsy is assigned a number according to the Gleason scale of 1 to 5. The number 1 indicates the “least aggressive” type of prostate cancer, and the number 5 represents the “most aggressive” form of the disease. The two most common numbers from the set are added together to determine the overall Gleason score.

For example, out of 12 tissue samples listed below, “2” is the most common ranking, while “3” is the second most common.

1   2   3   2   4   2

2   3   3   2   1   2

The two numbers are added together (with the most common number listed first in the equation) for a total Gleason score of 5.

2 + 3 = 5

A Gleason score of 1 and 2 is rarely seen. The most common overall Gleason score is 3, but it can range from 2 to 10. Essentially, when the two grades are added together, we arrive at a "Gleason score." Gleason 6 is generally referred to as a lower score, Gleason 7 an intermediate score, and Gleason 8, 9 or 10 is a higher score. In cases where the Gleason score is on the high side, additional tests such as an MRI, CT scan or bone scan will be conducted to help stage the prostate cancer more precisely,” Dr. Bevan-Thomas says. “Based on these reports, we then use the American Joint Committee on Cancer TNM staging system to describe how far the cancer has spread.

The TNM system is based on five important pieces of information:

  • T category: the extent of the primary tumor
  • N category: whether the cancer has spread to nearby lymph nodes
  • M category: the absence or presence of distant disease metastasis
  • The PSA level at the time of diagnosis
  • The Gleason score based on the prostate biopsy or tissue removed during surgery

There are actually two types of staging for prostate cancer—the clinical stage and the pathologic stage.

Clinical staging is your doctor's best estimate regarding the extent of the prostate cancer based on the results of a physical exam, digital rectal exam (DRE), lab tests, prostate biopsy and imaging tests.

Pathologic staging is based on the examination of tissue removed during surgery. Pathologic staging is likely to be more accurate than clinical staging because it enables physicians to get firsthand knowledge about the extent of the cancer.

Both clinical and pathologic staging use the same categories, however the T1 category is not used for pathologic staging.

T categories (clinical)

There are four categories for describing the local extent of a prostate tumor, ranging from T1 to T4. Most of these have subcategories.

T1:Your doctor can't feel the tumor or see it with imaging such as transrectal ultrasound.

  • T1a - The cancer was found by accident during treatment for benign prostate enlargement, but is present in less than five percent of the tissue removed.
  • T1b - The cancer was found during treatment for benign prostate enlargement, but is present in more than five percent of the tissue and has a higher grade Gleason score.
  • T1c - Cancer was found by a needle biopsy that was performed following an increased PSA.

T2: The cancer can be felt during a digital rectal exam and seen with transrectal ultrasound, but appears to be confined to the prostate gland.

  • T2a - The cancer is only found in one half or less than half of the left or right side of the prostate—not both sides.
  • T2b - The cancer is in more than half of only one side (left or right) of the prostate.
  • T2c - The cancer is in both sides of your prostate.

T3:The cancer has begun to grow and spread beyond the prostate, and may have spread into the seminal vesicles.

  • T3a - The cancer extends outside the prostate, but is not in the seminal vesicles.
  • T3b - The cancer has spread to the seminal vesicles.

T4: The cancer has grown into tissues next to the prostate (not the seminal vesicles) such as the urethral sphincter, rectum, bladder or pelvis wall.

N categories

N categories describe whether the cancer has spread to nearby lymph nodes.
NX: Nearby lymph nodes were not assessed.
N0: The cancer has not spread to any nearby lymph nodes.
N1: The cancer has spread to one or more lymph nodes in the pelvis.

M categories

M categories describe whether the cancer has spread to distant parts of the body. Most commonly, prostate cancer spreads to distant lymph nodes and to the bones—although it can also spread to other organs, such as the lungs and liver.

M0: The cancer has not spread past nearby lymph nodes.
 
M1 The cancer has spread beyond the nearby lymph nodes.

  • M1a - The cancer has spread to distant lymph nodes beyond the pelvis.
  • M1b -The cancer has spread to the bones.
  • M1c - The cancer has spread to other organs such as the lungs, liver or brain (with or without spread to the bones).

“Looking at all of this information—your PSA level, your Gleason score and T category—gives us a good look at your potential risk for high-grade prostate cancer, and how to best treat your individual cancer for the best possible outcome,” Dr. Bevan-Thomas says.

While every individual’s cancer case is unique, USMD Prostate Cancer Center routinely classifies men into risk categories according to guidelines established by the National Comprehensive Cancer Network (NCCN). The NCCN system takes Gleason grade, cancer stage, PSA, and the presence or absence of lymph node and bone involvement into consideration. In our next blog, we’ll cover the NCCN classification system—so stay tuned.

If you or a loved one have questions about next steps or treatment options following a PSA test, digital rectal exam or biopsy, talk with one of the board-certified urologists at USMD Prostate Cancer Center. Click to Request A Call Back or Call us today at 1-888-PROSTATE to schedule an appointment.

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