Understanding prostate cancer

What prostate cancer is, what your PSA, Gleason score and Grade Group mean, how risk groups and stages work, and the tests you may have.

5 min read · last reviewed September 30, 2026

A prostate cancer diagnosis brings a lot of new words at once: PSA, Gleason, Grade Group, risk group, stage. It can feel like a different language. The good news is that these words fit together into a simple picture, and that picture helps you and your team choose the right next step.

Here is a plain-language guide.

What is the prostate?

The prostate is a gland about the size of a walnut. It sits just below the bladder, in front of the rectum (the end of the bowel). The tube that carries pee out of the body, called the urethra, runs right through the middle of it. The prostate makes some of the fluid in semen. It needs male hormones, like testosterone, to grow and work.

Because of where it sits, prostate cancer and its treatments can affect peeing, bowel habits and erections. Your team will talk with you about this.

What is prostate cancer?

Prostate cancer starts when cells in the prostate grow out of control. Almost all prostate cancers are a type called adenocarcinoma, which starts in the gland cells.

Prostate cancer is not one single disease. Many prostate cancers grow slowly and may never cause problems. Others grow faster and can spread outside the prostate, most often to nearby lymph nodes or to the bones. Much of the testing you go through is about working out which kind you have.

PSA: what the number means

PSA stands for prostate-specific antigen. It is a protein made by the prostate, and it is measured with a simple blood test.

• PSA is not a cancer test on its own. It can also go up with an enlarged prostate, an infection, or even recent bike riding or ejaculation.
• The trend matters. Your team usually looks at how your PSA changes over time, not just one result.
• After treatment, PSA is a helpful tracker. It shows how well treatment is working and helps spot if cancer comes back.

Something you can do: Keep a simple list of your PSA results and dates. It makes it easier to follow along when your team talks about trends.

Gleason score and Grade Group

When you have a biopsy, a specialist called a pathologist looks at the tissue under a microscope. They see how much the cancer cells look like normal cells.

The Gleason score adds together two numbers for the most common patterns of cancer cells. You may see it written like "3 + 4 = 7." Today, 6 is the lowest Gleason score usually given to cancer found on a biopsy. So a score of 6 is the low end, not the middle.

To make this easier, doctors now also use the Grade Group, a single number from 1 to 5:

• Grade Group 1 (Gleason 6): the cells look close to normal. The cancer is likely to grow very slowly.
• Grade Groups 2 and 3 (Gleason 7): in between. Grade Group 3 is more likely to grow than Grade Group 2.
• Grade Groups 4 and 5 (Gleason 8 to 10): the cells look very different from normal. The cancer is more likely to grow and spread quickly.

Risk groups

Your team combines your PSA, Grade Group, and what the exam and scans show to put the cancer in a risk group. You may hear:

• Low risk: small, slow-growing cancer. Often a good fit for active surveillance.
• Intermediate risk: sometimes split into "favourable" and "unfavourable." Options vary.
• High risk or very high risk: more likely to grow or spread. Treatment is usually recommended.

Risk groups help your team compare options. They do not tell your personal story, and they are only one part of the decision.

Stages in plain language

The stage describes how big the cancer is and whether it has spread. Doctors use the TNM system (tumour, nodes, metastasis) along with PSA and Grade Group to give a stage from 1 to 4.

• Stages 1 and 2: the cancer is only inside the prostate.
• Stage 3: the cancer has grown through the outer layer of the prostate, or it has a high grade or PSA. It may reach nearby tissues, like the seminal vesicles.
• Stage 4: the cancer has spread to lymph nodes, or to other parts of the body such as the bones.

You may also hear "localized" (inside the prostate), "locally advanced" (just outside it) or "advanced" or "metastatic" (spread further). If cancer grows even while testosterone is kept very low, it is called "castration-resistant." That is a treatment term, and it does not mean treatment has run out.

Tests you may have

Digital rectal exam (DRE). The doctor gently feels the prostate with a gloved finger through the rectum. It takes less than a minute and can be a bit uncomfortable, but it shouldn't hurt.

MRI of the prostate. A scanner uses magnets to make detailed pictures. It helps find areas to biopsy and shows whether cancer may have grown outside the prostate. You lie still in a tube-shaped machine for about 30 to 45 minutes. Tell the team if you feel anxious in tight spaces.

Biopsy. A thin needle takes small samples of tissue, either through the skin between the scrotum and anus or through the rectum. You get medicine to numb the area. Afterwards, it's common to see a little blood in your pee, stool or semen for a few weeks.

Scans to check for spread. If your cancer is higher risk, you may have a bone scan, CT scan, or a PSMA PET scan. A PSMA PET scan uses a tracer that sticks to prostate cancer cells, which can help find small areas of cancer.

Genetic testing. Some people are offered testing for inherited gene changes, such as in the BRCA genes. This is more likely if your cancer is higher risk or has spread, or if prostate, breast, ovarian or pancreatic cancer runs in your family. Results can guide treatment and may matter for your relatives too.

Questions to ask your care team

• What is my PSA, and how has it changed over time?
• What is my Grade Group and Gleason score, and what do they mean for me?
• What is my risk group and stage?
• Do I need more scans, such as a bone scan or PSMA PET scan? Why?
• Should I have genetic testing? Should my family know about it?
• How much time do I have to make a treatment decision?

This article is general information, not medical advice. Talk with your health care team about your own situation. In an emergency, call 9-1-1 or your local emergency number.

In an emergency, call 9-1-1 or your local emergency number.

General information, not medical advice. It does not replace your own care team. If you think you or someone else is having a medical emergency, call 9-1-1 or your local emergency number. If you are in crisis or thinking about suicide, call or text 9-8-8 (Canada and the US).

Back to Prostate cancer