How is prostate cancer diagnosed?

Prostate cancer is diagnosed using a combined approach of considering symptoms, carrying out a physical examination, biopsies and scans.

Symptoms

Localised prostate cancer usually causes no symptoms at all. The following urinary symptoms are common in men over 50 and are due to pressure from the prostate on the urethra:

• passing urine more frequently
• difficulty starting and stopping when passing urine
• poor flow of urine
• getting up at night more frequently to urinate.

Although these symptoms are usually due to benign (not cancerous) prostate enlargement, it is important to have them checked by a doctor.

Sometimes prostate cancer can spread without these symptoms occurring. If this happens, the first symptoms may be pain in the groin, lower back, hip or upper thighs.

For more information on non-cancerous prostate enlargement, see Benign prostatic hyperplasia.

Diagnostic tests

A number of tests can be performed to confirm the diagnosis if your doctor suspects that you have prostate cancer. These tests will also check the size of the cancer and determine whether or not it has spread.

You may have some or all of the following tests:

Digital rectal examination (DRE)

The first test is usually an examination of the prostate gland through the back passage (rectum).This is called a digital rectal examination.

The doctor puts a gloved finger into your rectum and feels the prostate through the rectal wall. If your doctor finds anything suspicious, such as irregularity in the shape or texture of the prostate, a biopsy may be arranged.

Blood test (PSA)

A blood test may be done to check for the presence of prostate-specific antigen (PSA). There are many causes for a high PSA, including benign enlargement of the prostate and prostatitis but a high PSA can also be caused by prostate cancer.

An elevated PSA test merely indicates your risk of having prostate cancer is higher compared to a person with a normal PSA. A general rule of thumb is that if you have a PSA higher than four, the risk of cancer is sufficient to consider a biopsy.

The higher the PSA is above four, the greater the risk of cancer. However, in older men a higher PSA level may be considered normal.  If cancer is present, changes in PSA levels can be used to monitor whether the cancer is growing, staying the same, or shrinking.

Ultrasound examination and biopsy

In a biopsy, a sample of tissue is removed from the body. For a biopsy of the prostate, a small needle is directed into the prostate, guided by an ultrasound probe in the rectum, (this is called transrectal ultrasound or TRUS).

The probe is the size and shape of a middle finger and shows the shape and condition of the prostate. Usually six cores of prostate tissue are withdrawn from different parts of the gland and sent for examination under a microscope.

There will be discomfort associated with this procedure. Talk to your specialist about options for sedation. The biopsies are important to help you and your specialist make decisions about treatment.

How is the biopsy interpreted?

Tissue taken during the biopsy is looked at under a microscope. If there are malignant cells present, these are assessed for their aggressiveness. This assessment is called grading and the most common way of grading prostate cancer is to give the cells a Gleason score. Your specialist will use this information to help with decisions regarding treatment.

Gleason score

The Gleason grading system assigns a grade (indicated by a number from 1 to 5), to the most prominent pattern of cells in the cancer and another grade (1 to 5) to the second most common pattern. Grade 1 is the least aggressive cancer and grade 5 the most aggressive.

The two numbers are then added together to produce the Gleason score. The total score can be anywhere from 2 (1+1) to 10 (5+5).

What do the Gleason scores mean?

The scores measure differentiation, the medical term used to describe how closely cancer cells resemble normal cells. Well-differentiated cancer cells look very much like normal cells of the same type and are able to carry out some functions of normal cells.

Poorly differentiated and undifferentiated tumour cells are disorganised and abnormal looking.

As a general rule, the more the cells look like normal cells under the microscope, the slower growing they are. The greater the difference in the appearance of the cell from what is normal, the higher the number that is assigned on the Gleason score.

Interpreting Gleason scores

Gleason 2,3,4
Most like normal cells, well-differentiated, slow growing, low probability of metastasis,
low grade
Gleason 5,6,7
Can behave like normal cells or like aggressive cells, moderately differentiated, moderate
probability of metastasis, moderate grade
Gleason 8,9,10
Least like normal cells, poorly differentiated, high probability of metastasis, high grade.

Staging

Staging is a process of assessing the extent of a tumour. This information is gained by using the digital rectal examination, PSA blood test and information from the biopsies and ultrasound examination.

Tumours may:

• be confined to the prostate,
  
• be locally advanced, which means it has spread beyond the prostate but not to distant parts of the body,
• or metastatic, which means it has spread to other parts of the body.

While the Gleason score reflects what the cancer looks like under the microscope, the stage of the cancer reflects where the cancer is found.

Other tests such as a bone scan, lymph node dissection, or occasionally a CT scan (computerised tomography) may be used in some cases.

Bone scan

A bone scan may be used to look for any spread of cancer to your bones. A very small amount of radioactive material is injected into a vein to highlight small areas in the bone, which may contain cancer cells.

A scanning machine is then used to see if the radioactive material collects in any areas of your bones.

X-rays

X-rays of the chest and bones may be done to find out whether or not the cancer has spread to these areas.

CT scan (formerly called a CAT scan)

You may have a CT scan, although these scans are not commonly used in the diagnosis of prostate cancer. The CT scan is a special type of x-ray that gives a three-dimensional picture of the organs and other structures (including any tumours) in your body.

It usually takes about 30-40 minutes to complete this painless test.

Pelvic lymph node dissection

Your doctor may wish to operate to remove some of the lymph glands in your pelvis close to your prostate (pelvic lymph node dissection) in order to find out the extent of the prostate cancer. 

The gland will then be examined under a microscope to see if the cancer has spread through the lymphatic system.

This procedure can be done during laparoscopy (key-hole surgery) which avoids major surgery to open the abdomen, or during surgery to remove the prostate (radical prostatectomy).

Related topics

What treatments are there for prostate cancer? See Treatment of prostate cancer

What is prostate cancer? See Prostate cancer

Are there any issues about screening or treatment for prostate cancer? See Prostate cancer screening

What does that term mean? See Cancer glossary

Original material provided by the Cancer Society of New Zealand, 2001. Reviewed by everybody, February 2005.