reachout - I believe you would use 60% in the calculation, but I am not a doc and could be wrong. I base this on what I read in this article: jama.ama-assn.org/content/281/15/1395.long
(free) which is linked to from the nomogram. Excerpt below:
"The Stanford modified Gleason scale was used to estimate the proportion of each cancer that was poorly differentiated in all 379 radical prostatectomies.6 Briefly, from the Gleason scale of 5 grades,1 grades 4 and 5 (poorly differentiated) constitute a variety of histological patterns having the common feature that they do not form intact gland units mimicking normal architecture. Grades 4 and 5 contrast sharply with Gleason grades 1, 2, and 3, all of which form complete gland units and appear to have similar favorable prognostic significance.7 Accordingly, we combined grades 1, 2, and 3 into a single well-differentiated category. The percentage of each cancer occupied by Gleason grades 4 and 5 (% Gleason grade 4/5) was estimated by a single pathologist (J.E.M.) and performed prospectively before biochemical failure was detected by serum PSA findings. These % Gleason grade 4/5 data were compared with the Gleason scores, in which the 2 most prevalent grades in each cancer are added together and used as a sum or score. Most commonly, the score reflects 2 adjacent grades (ie, 3 + 4=7 or 4 + 3=7) or cancers of pure grade (ie, 3 + 3=6). For a score of 7, the proportion of Gleason grade 4 cancer may vary between 5% and 95% without altering the score (sum). To use the traditional Gleason scoring system, fractional areas of tumor less than 5% of the total tumor area should be ignored; if the secondary grade is less than 5%, the primary grade (most common) is simply doubled to obtain the score. "