Djin - It all depends on the details of the percentage calculation. GM’s value of G4 at 70% does not necessarily mean that 30% is 3 & 5 although it seems reasonable. A tumor could have normal cell zones within it so the actual cancer is only 70% of the defined lesion volume and it is all 4 with a trace of 5. Probably have to have the pathologist explain how they calculate it if GM wanted to know....
Mumbo, I think you may be confusing (a) the estimate of the percentage of PCa in the whole prostate (total amount of cancerous tissue divided by total tissue in the prostate (10-15% in GM's case) with (b) the overall Gleason score, which is based solely on the percentages of patterns 3, 4, and 5 in all
, but only, the cancerous tissue throughout the prostate
, regardless of whether one's cancer occupied, say, 10% or 90% of the prostate. It is a conglomerate or composite score and does not refer to any one lesion
(unless, of course, you have just one lesion). The extent of one's cancer in the prostate (a) is independent of the overall G score of the cancer present (b). In my case, e.g., I had 3% extent or involvement of PCa in my prostate, but the cancer itself was G9 (4+5) when the G patterns were evaluated across all my G9 and G10 lesions. Thus I was downgraded from a G10 biopsy score (the score of my worst biopsy lesion) to a G9 after RP. I don't believe normal tissue enters the calculation at all for the Gleason score (b), whereas it obviously does for the tumor burdon (a).
"Tumor" can refer to the collection of all malignant tissue, especially when used after a RP, rather than a single lesion. The prostate is somewhat of a special case: as we know, PCa is usually heterogeneous, presenting with multiple discrete lesions.GM's report explicitly states that the cancer was 70% pattern 4 and 1% pattern 5. That doesn't leave much doubt that the remaining % pattern 3 was about 29%, making it the 2nd most common pattern, so G7 (4+3) with tertiary 5
At least that is my understanding.
Here is one of several papers I was referring to earlier:Over half of contemporary clinical Gleason 8 on prostate biopsy are downgraded at radical prostatectomy
Another more recent study actually came up with an empirical rule for calculating the chances of being downgraded from a biopsy 4+4 to a 4+3 after RP: For every G7 lesion found in the biopsy you add percentage X (I think 17% but not certain) for each G7 lesion and you deduct percentage Y (I forget) for each additional G8 lesion over one lesion. In other words: Number of G7 lesions times X% minus [(number of G8 lesions -1) times Y%].
As I mentioned, 4+4 is a special case like 5+5: it takes just 5% or more of pattern 3 or 4, respectively, in the entire prostate for a downgrade. Thus the very high downgrade rates. (A post-RP path exam doesn't examine the entire prostate microscopically of course, but rather a representitive sampling throughout)
Post Edited (DjinTonic) : 5/28/2021 9:12:30 PM (GMT-6)