The challenge with biopsies, as Dr Walsh's book points out, is that they sample only a tiny % of prostate tissue, and they can sometimes miss very small tumours completely — almost literally a needle poking into a haystack. That's why diagnosis needs to be a multilayered approach, including digital rectal exams, imaging, blood work (especially PSA), genetic testing, and monitoring symptoms. The plan is that if the cancer slips through one net, it will get tangled in one of the others.

That said, biopsy is a pretty-good test once the cancer has formed large-enough tumours, especially if it's done at a facility that does hundreds or even thousands of prostate biopsies a year (you don't want to be just the prostate biopsy of the week or month, because they won't have the chance to develop their skills to the same extent).

In my case (which is atypical), they never biopsied my prostate at all. I had a lesion on my spine of unknown origin, so they biopsied it, then had to surgically remove it two days later because it was paralysing me. The surgeon said it felt like prostate cancer, the biopsy pathology result a couple of days later confirmed prostatic origin, and analysis of the tumour material itself backed up those conclusions. But I never had a needle poked into my prostate at all (just a DRE), so I didn't even get a Gleason score, though we know it's either 8 or 9 for a cancer that was aggressive enough to spread to my spine that fast.