How is prostate cancer diagnosed?

Dr. Mehmet Oz, MD
Cardiologist (Heart Specialist)

Prostate cancer is easy to detect with a rectal exam or a PSA (prostate-specific antigen) test. The test measures the level of protein in the blood produced by the prostate. If the levels are elevated, it could be an indicator of a simple infection or a tumor. This is why it's important for men to know what their normal PSA number is, says Dr. Mehmet Oz, Vice-Chair and Professor of Surgery at Columbia University. "You've got to get a baseline number. One of the big mistakes men get is they never get started. If you're 40 years of age, you ought to know what your PSA is."

Screening methods for prostate cancer include a digital rectal exam by a doctor to feel for any abnormalities in the prostate gland. Sceening for prostate cancer also includes a blood test, which tests for levels of prostate-specific antigen (PSA), a possible indicator that cancer is present.

If cancer is suspected, a doctor may order a biopsy and more advanced imaging of the prostate.

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There are two methods that physicians use to screen for prostate cancer. One of them is called a digital rectal exam. A digital rectal exam is done in your primary care physician's office. Because your prostate is so close to your rectum, your doctor can feel it by inserting a gloved, lubricated finger into your anus. Your doctor can feel if there are lumps, asymmetries, or if your prostate is enlarged. A digital rectal exam is uncomfortable, but not painful. Although it isn't a perfect test, it becomes more useful when it is combined with another test called a PSA.

The prostate gland produces a protein called prostate-stimulating antigen, or PSA.

Often, PSA levels will begin to rise before there are any symptoms of prostate cancer. Sometimes, an abnormal digital rectal exam may be the only sign of prostate cancer (even if the PSA is normal). If you have an elevated PSA, your doctor may have recommended a biopsy to tell if you have prostate cancer.

There are two main screening methods to detect prostate cancer. They have been shown to be most beneficial when used in combination. However, this is still very controversial, as screening has never been shown to decrease deaths due to prostate cancer. The first method is a blood test looking for something called prostate specific antigen, or PSA. PSA is a protein made by the prostate and can be found to be elevated in certain conditions, including in someone who has prostate cancer. The second is a digital rectal exam, in which the doctor performs a rectal exam to feel for any enlargement, firmness or nodules on the prostate. If you are considering being screened for prostate cancer, you should discuss with your doctor the risks versus the benefits of being tested.

The process of screening involves testing men who are apparently healthy and with no symptoms to identify those with a higher probability of having a disease, and who are then appropriate for further diagnostic testing.

Doctors estimate the significance of a cancer by estimating its stage—how far it has progressed. Doctors speak of two kinds of staging, clinical and pathological. Clinical staging is based on the analysis, under a microscope, of the samples of tissue taken during the needle biopsy. The pathological stage is what is found during prostate surgery, when the gland and the areas around it can be more carefully sampled, and is far more accurate. The purpose of clinical staging is to estimate the pathological stage. Staging is important because the cancer can no longer be cured by surgery if it has begun to spread beyond the capsule of the prostate.

The standard needle biopsy includes six cores (samples) taken from across the prostate, especially from suspicious areas seen on an ultrasound. The trend is to take more samples in hopes of improving the accuracy of clinical staging. This includes estimating how large the tumor is by the number of cores and the percentage of each that contain cancer cells. It also includes an evaluation of whether the tumor has penetrated the capsule of the prostate gland. This is done by examining samples from the margins of the prostate for cancer cells. Staging also includes an analysis of the grade of the cancer cells—that is, how different they are from normal cells. This gives an idea of how aggressive the cancer may be. A prostate-specific antigen level test is also used to estimate the significance of the cancer. The higher the PSA, the more extensive the cancer probably is.

Dr. Marc B. Garnick, MD
Hematologist & Oncologist

A Gleason score is a numerical grade that describes prostate cancer based on its aggressiveness—that is, how rapidly its malignant cells are multiplying. The higher the score, the faster the malignant cells are multiplying. Today, in practice, doctors almost never see a Gleason score of 2, 3, or 4; rather, the score usually ranges from 5 to 10. So, a Gleason score of 5 or 6 indicates a tumor that is on the slower-growing end of the scale.

In prostate cancer, once the tumor-node-metastasis (TNM) category, prostate-specific antigen (PSA) level and Gleason score have been determined, physicians consider that information and assign a stage grouping. The overall stage is expressed in Roman numerals from stage I (the least advanced) to stage IV (the most advanced). This helps physicians evaluate the probable course of the illness and the best possible approaches to treatment.

Prostate cancer often does not cause any symptoms in the early stages. Prostate cancer screenings make it possible to detect the cancer in early stages, before symptoms are present.

Current screening methods include a simple blood test for the prostate-specific antigen (PSA) and a digital rectal exam (DRE) of the prostate. Your doctor will assign a Gleason score (1-5) to the disease based upon its microscopic appearance. Cancer with a higher Gleason score is more aggressive. Together with other diagnostic tests, the Gleason score is incorporated into a strategy of prostate cancer staging, which helps guide therapy.

Although screening methods are not 100 percent accurate, these tests are often an effective method for detecting prostate cancer in the early stages, when it is still highly treatable. Talk with your doctor about whether or not prostate cancer screening is right for you.

The following tests are useful for detecting prostate cancer:

  • Digital Rectal Exam (DRE): Using a gloved, lubricated finger, the doctor examines the prostate to check for lumps or other abnormalities. If anything suspicious is found, additional testing may be needed.
  • PSA Test: Blood is drawn to test the amount of prostate-specific antigen (PSA), a protein made by the prostate gland and found in the blood. High PSA levels can be associated with prostate cancer.
  • PCA 3 Test: This relatively new test for prostate cancer measures levels of the prostate cancer gene 3 (PCA3) in urine. In some cases, this test may help diagnose prostate cancer in patients who have elevated PSA levels but a negative biopsy.

Once prostate cancer is diagnosed, the stage of cancer needs to be determined in order to decide on the most appropriate treatment plan. Staging is the process of determining if the cancer has grown within the prostate region or if it has spread to other areas of the body.

Three key factors are used to determine the cancer stage: T (the size of the tumor), N (if the lymph nodes are involved in the cancer) and M (if the cancer has metastasized, or spread, to other organs in the body).

Similar to other types of cancer, the outcome or prognosis of prostate cancer depends on whether or not it has spread when it is diagnosed. This is called staging. The American Joint Committee on Cancer (AJCC) TNM system is the most widely used staging system for prostate cancer. It is based on 5 key pieces of information:

  • The extent of the primary tumor (T category)
  • Whether the cancer has spread to nearby lymph nodes (N category)
  • The absence or presence of distant metastasis (M category)
  • The PSA level at the time of diagnosis
  • The Gleason score, based on the prostate biopsy (or surgery)
Dr. Michael R. Harrison, MD

By measuring the amount of prostate specific antigen (PSA) in a man's bloodstream, we can discover prostate cancer at earlier stages—giving men a better chance for survival. The test is not perfect. Some studies show that it misses up to 15 percent of cancer cases, while flagging some cancers so small and slow-growing that they pose no threat. Still, the PSA test remains the best clinically available tool for predicting prostate cancer. PSA screening is especially important for men with a family history of prostate cancer and for African-American men, who have a 60 percent higher incidence of the disease than whites.

Prostate cancer is generally detected and diagnosed through routine screening. Prostate cancer can often be detected even before symptoms begin to appear. There are two common tests for the disease: digital rectal examination, in which the doctor physically feels the prostate using a lubricated finger inserted through the rectum; and the prostate-specific antigen (PSA) test, which is a blood test. If either of these tests indicates the potential for prostate cancer further tests will be ordered, possibly including an ultrasound and a biopsy, or sample, of prostate tissue. A Gleason score can help determine treatment for prostate cancer based on how high the score is.

Although it is possible to detect and diagnose prostate cancer before symptoms appear, the practice remains controversial, as early detection of prostate cancer is not necessarily linked to higher survival rates. False positives may lead to stress and unnecessary treatment. While screening recommendations are still under review, since the ill effects of false positives can be life altering, and cancers of the prostate tend to grow slowly, it is recommended that doctors and patients ages 55-69 discuss the benefits and possible harms of PSA testing, so patients can understand and participate in the decision to undergo screening. Generally, men 70 and older should not be screened.

As with all suspected cancers, a tissue sample needs to be taken to make the diagnosis. Your urologist will perform an ultrasound and take a tissue biopsy from the prostate to make the diagnosis.

We are investigating the use of magnetic resonance imaging (MRI) for prostate cancer, but currently prostate cancer is diagnosed from the results of a biopsy. At least 20 percent of men diagnosed with prostate cancer annually have a low prostate-specific antigen (PSA), so the digital rectal examination (DRE) remains important.

Prostate cancer is detected via thorough and vigilant screening, typically as part of your yearly comprehensive physical examination. Annual screenings should begin at age 50 for the general population, age 45 if you have one risk factor or age 40 if you have more than one risk factor. Risk factors include, but are not limited to, being African American and having a familial history of prostate cancer. 
Screening tests fall into two categories: those that screen for prostate cancer and those that help determine the stage of the disease.

  1. Digital Rectal Exam (DRE) - an exam by a doctor who inserts a gloved, lubricated finger into the rectum to examine the prostate gland, looking for abnormalities in texture, shape or size.
  2. Prostate-Specific Antigen (PSA) Test - checks a blood sample for the level of PSA, a substance produced by the prostate gland. If a higher than normal value of PSA is detected (above 4.0ng/mL) it may indicate prostate infection, enlargement of the prostate gland, or cancer. Also, if measured over a long period of time, the rate at which your PSA rises can also be a red flag for prostate cancer.
  3. Transrectal Ultrasound - a small probe is inserted into the rectum which emits sound waves to produce an image of the prostate gland.
  4. Prostate Biopsy - using ultrasound for assistance, the doctor removes 6-12 cores (small pieces of the prostate) for pathological evaluation. These tissue samples provide a diagnosis of prostate cancer and the grading of the cancer. The biopsy and Gleason score are important in diagnosing and choosing the appropriate approach to treatment.

A Gleason score is the most commonly used grading system in the US. It is based on the appearance of prostate cells under a microscope. In assigning a grade to a tumor, a pathologist will assign a primary grade to the pattern of cancer that is most commonly observed and a secondary grade to the second most commonly observed pattern in the specimen. Gleason scores are always a combination of these 2 numbers. Grades range from 1-5, so scores range from 2-10 with higher scores indicative of more aggressive cancer. Primary Gleason grade is one of the most important factors to consider when predicting the outcome of disease.

Diagnostic equipment and surgical procedures may help detect and diagnose prostate cancer:

  • Transrectal ultrasound: a probe is inserted into your rectum to measure prostate volume and scan for tumor masses.
  • Transrectal ultrasound guided biopsy: a probe is inserted into your rectum where 8 to 12 small samples of prostate tissue may be taken for biopsy, which is a microscopic evaluation of potential cancer cells. A prostate biopsy is needed to confirm or rule out a diagnosis of prostate cancer.

If cancerous cells are found, they are rated from 1 to 5 using the Gleason system. The Gleason system assigns the cells a grade based on how the patterns, sizes, and shapes of the cells are different from healthy prostate cells.

A diagnosis of prostate cancer can be confirmed only by biopsy. During a biopsy, a urologist (a doctor who specializes in diseases of urinary and sex organs in men, and urinary organs in women) removes tissue samples, usually with a needle. This is generally done in the doctor's office with local anesthesia. Then, a pathologist (a doctor who identifies diseases by studying tissues under a microscope) checks for cancer cells.

Men may have blood tests to see if the cancer has spread. Some men also may need the following imaging tests:

Bone scan: A doctor injects a small amount of a radioactive substance into a blood vessel, and it travels through the bloodstream and collects in the bones. A machine called a scanner detects and measures the radiation. The scanner makes pictures of the bones on a computer screen or on film. The pictures may show cancer that has spread to the bones.Computerized tomography (CT) scan: An x-ray machine linked to a computer takes a series of detailed pictures of areas inside the body. Doctors often use CT scans to see the pelvis or abdomen.Magnetic resonance imaging (MRI): A strong magnet linked to a computer is used to make detailed pictures of areas inside the body.

This answer is based on source information from the U.S National Institutes of Health.  


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