What does it mean when there are different core samples with different Gleason Scores?

Cores may be samples from different areas of the same tumor or different tumors in the prostate. Because the grade may vary within the same tumor or between different tumors, different samples (cores) taken from your prostate may have different Gleason Scores. Typically, the highest (largest number) Gleason Score will be the one used by your doctor for predicting your prognosis and deciding treatment.