For many cancers, especially those that are likely to spread throughout the body, it is important to find out if the cancer has spread and where it has spread. This is called staging. Knowing the stage helps the doctor decide what kind of treatment is best and can help understand a patient's prognosis when diagnosed. Prostate cancer is divided into stages I through IV (one through four). Staging for prostate cancer also includes measuring the prostate-specific antigen (PSA) level in the blood, and determining the grade, called a Gleason score. The grade of a cancer is a way of describing how much the cancer cells look like normal cells by looking at them under a microscope; a lower grade looks more like normal cells and a higher grade looks less like normal cells. In prostate cancer, lower-grade tumors are generally much less dangerous than higher-grade tumors. A low grade prostate cancer is defined as a Gleason score of six or less. Find more detailed staging information for prostate cancer .
If the prostate cancer is thought to have spread, doctors can use diagnostic tests, such as imaging tests (tests that create pictures of the inside of the body) to help find out if or where in the body a cancer has spread. These can include computed tomography (CT or CAT) scans  and positron emission tomography (PET) scans , as well as bone scans to find out if the cancer has spread to the bone.
ASCO recommends that the following imaging tests are not used for staging a low-grade cancer in people who also have a PSA level of less than 10 ng/ml:
- CT scan
- PET scan
- Bone scan
Research on these tests has shown that they do not help lengthen lives because most low-risk tumors don't spread so these tests are usually not necessary.
What this means for patients
CT, PET, and bone scans can be helpful tools in the right situations, such as for people with later-stage prostate cancer that is more likely to have spread, because they can show abnormal-looking areas in parts of the body that cannot ordinarily be seen or felt. It's important to remember that not all abnormal-looking areas in the body are cancerous. If an abnormal area is found on these tests, more tests are sometimes needed to find out if it is actually cancerous. For people with early-stage, low-risk prostate cancer that is unlikely to have spread, having these tests can often add extra procedures, more worry, and higher costs without improving or lengthening their lives.
Questions to ask your doctor
- What stage of prostate cancer do I have?
- How is the stage determined?
- What tests do I need to determine the stage?
- Will imaging tests be needed? Why or why not?
- What other information would these tests provide that could help determine my treatment options?
- What is the cost of each test?
- I have low-grade prostate cancer with a low risk of spreading, can you explain if there is any benefit to having certain imaging tests?
For More Information
Consumer Reports: Imaging Tests for Early Prostate Cancer  (Topic 2; PDF)