What does a Gleason rating of 8 mean?

Cancers with Gleason ratings between 8 and 10 are said to be poorly differentiated and typically grow and spread more quickly. Six is the lowest Gleason score and represents low-grade cancers that are less aggressive, while a score of 7 represents an intermediate cancer, notes the American Cancer Society.

Pathologists assign a prostate cancer Gleason score by analyzing cancerous tissue samples under a microscope and determining how much the cancerous tissue looks like normal prostate tissue. They judge this on a scale of 1 to 5 for two samples from different areas of the cancerous tissue. The Gleason score is obtained by adding the scores derived from the two samples, explains American Cancer Society.