The percentages that you read are the percentage of the core sample that was viewed as positive by the pathologist for prostate cancer. A typical pathology report has the size of each sample described. Usually the samples vary in size but they are usually described in the pathology report. When the pathologist detects the presence of cancer he tries to determine the percentage of each core in volume that is positive. You can get some variations from pathologist to pathologist and this is part of what makes a second opinion important. The pathologist usually also tries to determine the Gleason Grades that are present and some reports state what percentages he viewed of each grade. For example a pathologist has given to a patient a Gleason Sum os 3+4=7 with a presence of 35% in the sample. He made the determination that he saw more presence of grade 3 tumor that Grade 4 tumor. The percentage of each is not always listed but some reports do estimate this as well. Once again this is where not all pathologists agree.
Many protocols for active surveillance define limits to the percentage of positive cores when outlining a good candidate for AS. Also in advanced cases the high number of presence can lead doctors to recommend a local therapy with added adjuvant therapies or suggest only doing systemic therapies.
Advanced Prostate Cancer at age 44 (I am 49 now)
pT3b,N0,Mx (original PSA was 19.8) EPE, PM, SVI. Gleason 4+3=7
Da Vinci Surgery ~ 2/16/2007
Adjuvant Radiation Therapy ~ IMRT Completed 8/07
Adjuvant Hormone Therapy ~ 28 months on Casodex and Lupron.