What is prostate cancer?
Prostate cancer is one of the most common types of cancers in men. The prostate gland, which exists only in men, is involved in the production of semen. Cancer in the prostate often grows very slowly and remains within the gland.
In some instances it can be more aggressive, which means it grows quickly and can spread beyond the prostate. Many factors will determine the best treatment plan, including the stage of the cancer, PSA level, grade of the tumor (i.e., Gleason score), age of the patient, and the patient’s other health issues.
Prostate-specific antigen (PSA)
The prostate gland makes a protein called prostate-specific antigen, or PSA. A healthy man without prostate cancer should have a small amount of PSA circulating in his blood.
Some conditions related to the prostate can cause the gland to produce more PSA than normal. These include prostatitis, benign prostatic hyperplasia (enlarged prostate), and prostate cancer.
The PSA test
A PSA test is a test that measures the levels of the protein in the blood. The results are typically given in nanograms of PSA per milliliter of blood (ng/mL). A measurement of 4 ng/mL is considered to be normal, but this baseline changes with age. As a man ages, his PSA levels naturally rise. According to the National Cancer Institute (NCI), many organizations caution against routine PSA testing to screen for prostate cancer in average risk men. However, PSA testing can be used to help diagnose prostate cancer, determine a prognosis for those who have prostate cancer, and track progression of the cancer or response to treatment.
Staging prostate cancer
Staging of prostate cancer is used to communicate how advanced the disease is and to help plan treatment. Stages range from 1 to 4, with the disease being most advanced in stage 4. There are a number of factors that go into this labeling.
Prostate cancer, like many other cancers, is described based on the American Joint Committee on Cancer (AJCC) TMN staging system. This staging system is based on the size or extent of the tumor, the number of lymph nodes involved, and whether or not the cancer has spread or metastasized to distant sites or organs. Prognostic groups are further determined based on two additional factors: the PSA level and the Gleason score.
The role of PSA in staging
PSA levels are just one factor used in determining the stage and prognostic groups of prostate cancer.
Some men who have prostate cancer do not exhibit elevated PSA levels, and some noncancerous conditions, like a prostate infection or benign enlargement, can cause high PSA levels.
Stage 1 prostate cancer is characterized by a Gleason score of less than 6: the cancer is restricted to one half of the prostate with no spreading to surrounding tissues and a PSA level below 10. The Gleason score compares cancer cells to normal cells. The more the cells differ from normal cells, the higher the score and the more aggressive the cancer. Like the PSA level, it is just one piece of the puzzle.
In stage 2A prostate cancer, the tumor is still restricted to one side of the prostate, but the Gleason score may be up to 7, and the PSA levels are greater than 10 but less than 20 ng/mL.
By stage 2B, the tumor may have spread to the opposite side of the prostate gland, but it also may still be contained on one side. If the tumor is still restricted to one half of the prostate, a Gleason score of 8 or higher or a PSA level of 20 or greater categorizes the cancer as stage IIB. If the tumor has spread to both sides of the prostate then the stage is IIB regardless of the Gleason score and the PSA level.
Stages 3 and 4
By the time prostate cancer has reached stage 3 or stage 4, the cancer is very advanced. At this point, the stage is determined by the extent of the spread of the cancer, and the PSA level and Gleason score do not factor in the staging. In stage III the tumor has grown through the prostate capsule and may have invaded nearby tissue. By stage 4 the tumor is fixed or immovable and invades nearby structures beyond the seminal vesicles. It may also have spread to distant sites like lymph nodes or bones.
To determine the size and extent of the prostate tumor, doctors use imaging techniques like CT scans, MRIs, PET scans, and biopsies of prostate and other tissue.
Controversy over PSA levels
PSA tests are one tool used to stage prostate cancer, but as a screening tool it’s controversial and not always recommended. Research has proven that using PSA to screen for cancer does not save lives. On the other hand, it can cause harm by leading to more invasive procedures — like biopsies and surgery — that may not be necessary and can have complications and side effects. For this reason, the NCI cautions against the routine use of PSA screening for men at average risk of getting prostate cancer.
It may be a useful tool for high-risk men, especially African-Americans or those with a family history of prostate cancer. If you are considering PSA screening you should understand the risks and benefits of this test. PSA testing does remain, however, an important tool in staging and monitoring prostate cancer once it has been diagnosed and helping assess response to treatment.