Gleason score for prostate cancer: What to know about Biden's diagnosis

Joe Biden has been diagnosed with an "aggressive form" of prostate cancer.

Biden's team shared a statement on Sunday that the former president was experiencing "increasing urinary symptoms" ahead of his diagnosis, which was characterized by a Gleason score of 9 (grade group 5) with "metastasis to the bone."

"While this represents a more aggressive form of the disease, the cancer appears to be hormone-sensitive, which allows for effective management. The president and his family are reviewing treatment options with his physicians," the statement said.

JOE BIDEN DIAGNOSED WITH 'AGGRESSIVE FORM' OF PROSTATE CANCER WITH METASTASIS TO THE BONE

Biden's ranking of 9 on the Gleason scale, a grading system for prostate cancer severity, has sparked concerns, as it correlates with high-grade cancer.

Dr. Arpeet Shah, a urologist with Associated Urological Specialists in Illinois, explained in an interview with Fox News Digital how the grading system indicates the aggressiveness of the disease.

"It's based on what the cancer cells look like under a microscope - specifically, how different they look from normal prostate cells," he said. (Shah was not involved in Biden's care.)

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Pathologists assign two numbers from 1 to 5, based on the most common and second-most common patterns present in the tissue.

The lower the grade, the more normal the cancer cells look, according to Cleveland Clinic.

Descriptions of the grades are listed below.

Grade 1 - Cancer cells look like normal cells.

Grades 2 to 4 - Cancer cells in the tissue look less like normal cells.

Grade 5 - Cancer cells look very abnormal.

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The largest areas with cancer are graded and then added together to determine a Gleason score, which typically ranges from 6 to 10.

"The higher the score, the more aggressive the cancer is likely to be," Shah said.

Below is a breakdown of Gleason score ranges.

Gleason score of 6: Cancer is low-grade and slow-growing.

Gleason score of 7: Cancer is intermediate and more likely to grow or spread over time.

Gleason score of 8 to 10: Cancer is high-grade and may need more aggressive treatment.

The system is "one of the key tools" experts use to "help guide treatment decisions and to have meaningful conversations with patients about their options," Shah commented.

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"It's important to highlight the importance of 'early' here," he said. "Had President Biden undergone regular prostate cancer screening with a PSA blood test and digital rectal exam, his diagnosis might have been detected sooner."

In an appearance on "The Big Weekend Show" on Sunday, Fox News medical contributor and board-certified radiologist Dr. Nicole Saphier noted that much like breast cancer, prostate cancer comes in different forms and can be treated "very differently" per case.

Saphier confirmed that Biden's metastasized cancer is stage 4, which "significantly" decreases the chance of survival.

"No two cases are exactly the same," she said. "But the one good thing that they did mention about President Biden's case is that it's hormone-sensitive."

This form can be treatable through surgery or medication that will stop the testosterone production that fuels cancer growth.

"[Stage 4] is the worst-case scenario when you're talking about cancer, but we have so many treatments these days that you can actually live for quite a long time with stage 4 cancers," Saphier said.

"In his case, because it is hormone-sensitive, there are treatment methods," she continued. 

"It's never going to cure him. He's never not going to have stage 4 cancer. But he could get to the point where he has no evidence of disease or certain no progression of disease. And at this point, that's what our goal is."

Fox News' Stepheny Price and Peter Doocy contributed to this report.