To @kenkl1962
There are two reasons why the biopsy is a "12-core" sample process and in comparison to what happens to your prostate in the pathology lab after it is removed:
1) Although using an ultrasound-guided wand/probe, the urologist is collecting biopsy samples kind of blind. Through the DRE and perhaps a pre-biopsy MRI (if that happened) the urologist has a good idea where to biopsy, but they are also making sure they get all four main quadrants of the prostate: anterior, posterior, superior, and inferior in layman's terms. They likely needle-sample two maybe three cores from the same general area that they know is most likely cancerous.
2) While the needle looks long, the prostate is only the size of a walnut ("give or take"...age dependent getting bigger the older we get). The narrow-bore needle doesn't capture a lot of tissue...enough to expel into the jar of formalin preservative, but it is nothing like happens when the pathologist and histotech slice and dice your entire prostate after it has been removed. And...
The Biopsy is a "cytological" procedure. The tissue expelled into and from each sample jar is removed and put in an odd looking plastic contraption with a little funnel and a microscope slide inserted vertically. That is placed in a cytocentrifuge which spins the liquid with cells at a super-high rpm to deposit the cells on the microscope slide. Then the microscope slide is "fixed" and stained, after which the pathologist (usually) examines each slide...all twelve. They do one "pass"...a complete scanning of the entire slide, looking at the predominate type of cancer cells. This is the first number in your Gleason Score, say a "3." Then the pathologist re-scans the same slide looking for the second most-predominant cell type, say a "4". So, you end up with a 3+4=7 Gleason Score. Because some of your core samples will likely be negative/normal tissue (hopefully), your biopsy report will be a mix of what mine was for example: 3 cores normal/negative (no cancer); 3 cores that were Gleason 3+3=6; and 6 cores that were Gleason 3+4=7. Now...
3. Your surgically-removed entire prostate gland is sent to the the pathology lab, where the experienced eyes and skills of a licensed Histotech (in larger hospitals), or the pathologist themselves visually examines the cancerous prostate, and they dissect and remove areas that look most diseased. This is a "histologic/anatomical pathology" procedure. These small chunks of prostate tissue are put in paraffin blocks: hot liquid paraffin is poured over them in little tray like gizmos to give a block shape to them. Then...those blocks are placed on a microtome: think "meat cutter" in a sandwich shop that slices your turkey or roast beef into thin slices, but...the microtome slices in ultra-thin sections of the tissue, and they come off the microtome like a ribbon...all sequentially connected. Then the thinly sliced prostate tissue still surrounded by an ultra thin amount of paraffin, are put in a countertop hot water bath, where the paraffin sections are floated onto microscope slides and the paraffin melts away. There are a few little things that happen in and around each step, but those are the basics. So, ultimately, small, ultra-thin "sheets" of prostate tissue are mounted and fixed to "MANY" microscope slides. The slides are stained, and they are examined by the pathologist who can now see the much broader view of the entire prostate tissue and disease process, vs the smaller collection of cells seen in the biopsy.
The biopsy is sufficient to basically say: "You have cancer" or "You don't have cancer", and if you do, the Gleason Score reflects the maturity and progression of the cancer cells. But...they are just cells..."many" cells...but not "sheets of tissue" like happens to your post-Prostatectomy sample. The sheets of prostate tissue allow visualization of what may be EPE, surgical margins, cribriform glands, seminal vesicle invasion, Intraductal carcinoma, etc. And...
All of this, especially on biopsies, is why "so much" pathology and micro-anatomical features of your cancer are not revealed, and why we are all surprised when the post-prostatectomy pathology report comes out with all of the unexpected stuff, again, EPE, surgical margins, cribriform glands, seminal vesicle invasion, Intraductal carcinoma, etc
I hope this helps. It is pretty interesting stuff.