All of the following statements are TRUE about Gleason score, EXCEPT:

When prostate cancer is diagnosed, a measure of histologic aggressiveness is assigned using the Gleason grading system, in which the dominant and secondary glandular histologic patterns are scored from 1 (well-differentiated) to 5 (undifferentiated) and summed to give a total score of 2-10 for each tumor. Well-differentiated tumors have a Gleason sum of 2-4, moderately differentiated tumors have a Gleason sum of 5-6, and poorly differentiated tumors have a Gleason sum of 8-10. To better assess risk and guide treatment selection, a combination of the initial T stage, Gleason score, and baseline PSA are used, Ref: Scher H.I. (2012). Chapter 95. Benign and Malignant Diseases of the Prostate. In D.L. Longo, A.S. Fauci, D.L. Kasper, S.L. Hauser, J.L. Jameson, J. Loscalzo (Eds), Harrison's Principles of Internal Medicine, 18e.