Not correct.
Gleason score is used to GRADE the cancer; staging is a different matter and is determined by blood work, x rays and physical exam.
The Gleason score is a number or numbers given based on findings in a pathology exam of a prostate biopsy. The Gleason score is used to stage prostate cancer, and provide a rough prognosis. Higher numbers mean more cancerous cells doing more things, but there are important details worth knowing. See the entry on Wikipedia, on Prostate-Cancer.org, or similar sites for lots of details.