How is Prostate Cancer Measured?

Men diagnosed with prostate cancer often ask, how is prostate cancer measured? The most commonly used system to measure prostate cancer is the American Joint Committee on Cancer TNM system. This approach helps physicians and patients monitor and treat prostate cancer. Here’s an answer to how prostate cancer is measured.

Prostate cancer stages

The TNM system is based on five factors.

“T” refers to tumor. Experts have assigned a number from 1 to 4 to describe how far the tumor has developed based on a digital rectal examination (DRE). The higher the number, the more the tumor has developed. For example:

  • T0 means there is no evidence of a prostate tumor
  • T1 means the prostate tumor cannot be felt by the physician during a DRE or viewed using diagnostic imaging. However, the tumor may have been discovered during a prostate biopsy or surgery for an enlarged prostate.
  • T2 means the physician felt the tumor during DRE, but believes the cancer is limited to the prostate gland. There are subdivisions within T2: T2a means the tumor involves half or less of one side of the prostate; T2b means the tumor affects more than half of one side only; and T2c means the tumor has affected both sides of the prostate gland
  • T3 means the prostate tumor involves the prostate capsule and may also affect the seminal vesicles. The seminal vesicles are a pair of organs that secrete fluid that is part of semen. T3a means the tumor has reached beyond the prostate capsule but has not affected the seminal vesicles. A T3b tumor has extended to the seminal vesicles.
  • T4 designates a tumor that has invaded other structures (other than the seminal vesicles), such as the rectum, pelvic wall, or bladder.

“N” refers to whether the prostate cancer has spread to the lymph nodes. An N0 designation means the cancer has not advanced, and an N1 means it has reached one or more lymph nodes in the pelvic area.

“M” refers to metastasis, which is the spread of the cancer to areas beyond the prostate gland. A designation of M0 means the cancer has not spread, while M1 means it has extended beyond the prostate to the bones or other sites. Within this category, M1a means prostate cancer has spread to lymph nodes; M1b means cancer has reached the bones; and M1c means prostate cancer has spread to other organs, with or without involving the bones.

The other two components of the TNM system are the PSA level at the time prostate cancer is diagnosed, and the Gleason score, which is based on the findings of the prostate biopsy or surgery. Generally, a PSA level of greater than 4 ng/mL is considered an indication a prostate biopsy should be done.

The Gleason score can range from 2 to 10, and the higher the number, the poorer the prognosis. For example, scores of 2 to 5 indicate low-grade prostate cancer; 6 to 7 are intermediate prostate cancer; and 8 to 10 is an indication of high-grade prostate cancer.

When doctors combine all this information, they have a better indication of how prostate cancer is measured and a patient’s prognosis. Generally, there are 4 stages of prostate cancer:

  • Stage I prostate cancer is limited to the prostate and usually grows slowly. The Gleason score is 6 or less and the PSA is less than 10.
  • Stage IIA and IIB prostate cancer are cancers that cannot be felt or detected on imaging tests. Although prostate cancer has not spread beyond the gland, the cells are typically somewhat abnormal and may grow more rapidly than normal cells. For stage IIA, PSA levels are higher than 10 and Gleason scores are 6 or less, or PSA is less than 20 and the Gleason score is 7. For stage IIB, the Gleason score can be anything and the PSA level is greater than 20, or the Gleason score is 8 or greater regardless of the PSA level.
  • Stage III describes prostate cancer that has spread beyond the prostate to adjacent tissues and possibly to the seminal vesicles. Men who have reached this stage of prostate cancer can have any Gleason score and PSA level.
  • Stage IV is prostate cancer that has spread to other parts of the body, including the lymph nodes, liver, and bones. The Gleason score and PSA level can be at any figure.

Recognizing and understanding how is prostate cancer is measured can help patients and their healthcare providers make better decisions about how to treat the disease. Be sure to ask your healthcare provider questions about how prostate cancer is measured so you can then tackle choosing your treatment for prostate cancer.

Read more in our Prostate Cancer Health Center.