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The most commonly used tumor grading system is Gleason grading. Given that the individual Gleason value can range from 1 to 5, the added values (Gleason scores or “sums”) can range from 1+1 to 5+5 or from 2 to 10. Generally, Gleason scores of 2 to 4 are uncommon; as a result, the majority of detected tumors range from 5 to 10. Gleason 8 and above is considered high and the cancer likely to be more aggressive.
Tumor stage refers to the degree to which the tumor has involved the prostate gland or has spread. As with other tumors, prostate cancers that involve only a small portion of the prostate are more successfully treated than those that have extended throughout the gland.
Life expectancy, rather than patient age, is a major factor to consider in treatment selection.
Gleason score and tumor stage are predictive of cancer outcomes. Using PSA, Gleason score, and tumor stage, risk strata can be defined that predict possible cancer recurrence and cancer-specific mortality. Your doctor can advise you about how your specific risk characteristics may affect your decision regarding treatment.
(Source: American Urological Association)