Even if cancer cells are found, remember that all cancer cells are not the same. They can differ widely in their severity or aggressiveness. The pathologist will grade the cancer cells they find. They are measuring how much the cancerous prostate differs from normal prostate tissue. The pathologist assigns a grade to the most common tumor pattern, and a second grade to the next most common tumor pattern. The two grades are added together to get a Gleason Score. For example, if the most common tumor pattern was grade 3, and the next most common tumor pattern was grade 4, the Gleason Score would be 3+4 = 7. The Gleason Score ranges from 2 to 10, with 10 having the worst prognosis. For Gleason Score 7, a Gleason 4+3 is considered a more aggressive cancer than a Gleason 3+4.
The higher the grade, the more likely it is that the tumor will grow quickly and spread. Your doctor uses the tumor grade along with things like your age and overall health to decide how best to treat you.