What Is Gleason 6 Prostate Cancer?

When prostate samples are examined under a microscope, lab professionals (pathologists) look to see how closely the cells resemble those of normal tissue. They rate the samples on a scale of 3 (most similar to healthy tissue) to 5 (least similar), then add the two most common grades together to determine what's called the Gleason score.

Gleason 6 is the lowest grade possible. This rating means that the prostate cancer is considered to be low- or very low-risk disease, or group 1. Most of these tumors are found during routine prostate cancer screenings.

Gleason 6 prostate tumors grow slowly and may never cause a problem—or even need treatment. Still, they should be monitored.

Lab technician examining sample under microscope

Noel Hendrickson / Getty Images

This article outlines what Gleason 6 prostate cancer means, why monitoring is important, when treatment may be considered, and questions you can ask your urologist if you’ve been diagnosed.

The Gleason Grading System

Screening for prostate cancer involves the prostate-specific antigen (PSA) test and a digital rectal exam. If results are suspect, your doctor may recommend a prostate biopsy—the only way to confirm the diagnosis.

During a prostate biopsy, a urologist uses a small needle to remove tissue samples (usually 12) from different parts of the prostate. These samples—also called “cores”—are then sent to a pathologist so they can review each one under a microscope.

The pathologist uses a pattern scale, developed by Donald Gleason, MD, PhD in 1966, to give each sample a grade from 1 to 5. Grade 1 cells are “well-differentiated” and look like normal tissue. Grade 5 cells, on the other hand, are "poorly differentiated" or even unrecognizable from normal tissue.

Your Gleason score is the sum of the two numbers that represent the most common types of tissue found in your biopsy. The first number in the equation is the most common grade present, the second number is the second most common grade. For example, if seven of your cores are grade 5 and five are grade 4, your Gleason score would be 5+4, or a Gleason 9.

Today, pathologists typically only flag tissue samples that are grade 3 or higher, making 6 the lowest Gleason score.

In 2014, a revised grading system for prostate cancer—called Grade Groups—was established. This system builds on the Gleason scoring system and breaks prostate cancer into five groups based on risk. This can help make it easier to understand the Gleason score scale.

Prostate Cancer Grade Groups
 Gleason Score Grade Group Risk Group
 Less than 6  1  Low/very low
7 (3+4)   Favorable
 7 (4+3)  Unfavorable
 8  High
 9-10  Very high

Your Gleason score tells your care team quite a bit, including:

  • Whether cancer is present in your prostate
  • How quickly it is growing
  • How likely it may be to spread to other parts of your body

This helps you work with your urologist to make informed decisions about next steps.

What Does Gleason 6 Mean?

A Gleason score of 6 is different from other prostate cancer diagnoses because it means all the biopsy samples are grade 3 (3+3=6). Though the samples don’t look like normal tissue, no grade 4 or 5 samples were found.

Gleason 6 prostate tumors are:

  • Small
  • Confined to the prostate
  • Not causing any symptoms

There are changes at the cellular level, but the prostate cancer is likely slow-growing and has a low-risk of metastasizing, or spreading to other areas of the body.

This knowledge allows your doctor to monitor you and see how your tumor changes over time.

Cancer Controversy

There are some experts who say that Gleason 6 prostate tumors should not be called "cancer" because of their low-risk nature and the fact that the term may cause some patients to be overtreated.

This, however, runs counter to the stances of major medical organizations.

Terminology aside, the bottom line is this: Though not all prostate cancers require active treatment right away, your doctor can’t monitor a tumor if they don’t know it’s there.

Monitoring and Treatment Decisions

In the past, men with prostate cancer—regardless of whether it was aggressive or not—were almost always treated right away with a targeted therapy like surgery or radiation. However, in recent years, experts have revisited this “one-size-fits-all” approach to prostate cancer.

Experts now understand that low-risk prostate cancer—like Gleason 6 tumors–may not need treatment right away. In fact, major medical associations, including the American Urological Association and the Society for Urologic Oncology, now recommend the use of active surveillance for low-risk prostate cancer.

Watch and Wait

Though it is sometimes called “watchful waiting,” active surveillance doesn’t mean that you do nothing but sit and wait. Instead, it means your doctor will monitor your tumor over time with periodic PSA tests, digital rectal exams, and biopsies to see if it changes.

Watching the tumor closely will allow your doctor to step in when necessary so they can treat your tumor before it has a chance to spread to other parts of your body. Your urologist will work with you to determine how often each of these tests should be done to ensure that your tumor is being appropriately monitored.

Studies have shown men with low-risk disease on active surveillance continue to show good results even after a decade or more.

Postponing therapy until it’s necessary allows you to maintain your normal lifestyle and avoid potential side effects of prostate cancer treatment, such as incontinence or erectile dysfunction.

Recap

Because Gleason 6 prostate cancer is the least-risky type of prostate tumor, it doesn’t always need to be treated right away. Active surveillance is a way for your doctor to monitor your tumor’s progress to determine if and when treatment is really necessary.

When a Gleason Score Increases

If your Gleason score changes while you’re on active surveillance, it’s time for a discussion with your urologist to better understand the situation.

You may find it helpful to ask these questions:

  • In what way did my Gleason score increase? Remember that the numbers that comprise your Gleason score represent the two most common grades of tissue in your biopsy. Finding out which number increased is important to understanding how your tumor has changed. A change in your first number (for instance, a new Gleason score of 4+3) means that most of your tissue samples are now grade 4 (higher risk). A new Gleason score of 3+4 means that grade 3 (low risk) is still the most prominent type of tissue in your biopsy.
  • How does this impact my risk level? Your risk level is based on the distribution of grade 3 and grade 4 samples. A Gleason 7 (3+4) has a more favorable risk level than a Gleason 7 (4+3).
  • Is it time to consider active treatment? It can be unsettling to find out that your prostate cancer has changed or may be getting worse. However, even if your urologist recommends staying on active surveillance, it may bring you peace of mind to better understand at what point you’ll need to consider other options.

Summary

Gleason 6 prostate cancer is one of the most commonly diagnosed types of prostate tumor. It is the most low-risk type of the disease.

Because Gleason 6 is not likely to be aggressive or spread rapidly, active surveillance—monitoring for changes—is often used to watch the cancer over time. This allows a patient to put off treatment, such as surgery or radiation, until it is absolutely necessary.

Frequently Asked Questions

What is a Gleason score?

After a prostate biopsy, a pathologist looks at each sample under a microscope to see how closely they resemble normal prostate tissue and grade them on a scale of 1 to 5. Your Gleason score represents the two most common scores for tissue found in your biopsy. Because pathologists tend to only flag samples that are grade 3 or higher, the lowest score for prostate cancer is Gleason 6.

Is a Gleason score of 6 bad?

Not necessarily. A Gleason score of 6 means that all of the tissue samples in your biopsy were grade 3. This means that the cells are not normal, but aren’t necessarily aggressive or causing a concern.

How accurate is a Gleason score?

Pathologists and urologists have been using the Gleason system to grade prostate cancer for more than 50 years. It remains a powerful tool, particularly for low-risk disease.

One study showed it was more than 80% effective in identifying Gleason 6 cancers.

A Word From Verywell

Prostate cancer is the most common cancer affecting American men. One in eight men will be diagnosed with it in their lifetime. In 2021, nearly 250,000 men will be diagnosed with the disease.

The U.S. Preventive Services Task Force (USPSTF) recommends that healthy men ages 55 to 69 talk to their doctors about whether prostate cancer screening is right for them. If you have an elevated PSA test, your doctor may recommend a biopsy to confirm whether cancer is present.

If you go on to have a biopsy and have Gleason 6 prostate cancer, you may be tempted to “just get rid of it” by being treated instead of taking a watch-and-wait approach. As you weigh your decision, remember that most Gleason 6 prostate cancers grow very slowly and may never spread or cause problems.

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