The mathematics of screening diseases can be rather demanding.
The issues with prostate cancer aren’t so much about the screening, but are about the consequences of a positive screen.
If a positive screen leads to a positive biopsy, then one of two things happens:
“Watchful Waiting,” where the patient gets to live with a tumor and waits to see if it gets agressive.
Resection of the tumor, which may or may not lead to collateral damage of some rather important nerves, and which may lead to incontinence and/or impotence.
Radioactive “seeding” of the tumor, where small capsules of radiologically active material are placed within the tumor itself. This procedure may represent a less risky alternative to resection. But it isn’t a guaranteed treatment either.
Diagnostically speaking, it isn’t easy to distinguish prospectively between prostate lesions that will be well-behaved, slowly growing, non-metastatic creatures (with presentation similar to BPH) and those that are rapidly growing, metastatic cancers.
So a patient with a prostate cancer can either respond aggressively, or passively wait out the lesion. In many, many cases, the detected lesion is a slow growing lesion. In a few of these detected lesions, a slow growing lesion will flip out at some point and go aggressive. In cases in which a lesion is captured in an advanced state, it isn’t clear whether the lesion started out aggressively, or flipped at some point.
The slow growing cases are a bit like BPH - except in BPH, cancer isn’t involved. Unless, of course, the BPH is in reality misdiagnosed prostate cancer.
At some point, someone will develop a trans-prostatic stent, which would be deployed between the prostate gland and the urethra - this would fix some of the continence issues.
But the unfortunate extremes here are to either ignore a potentially dangerous cancer, or to needlessly watch over a basically harmless lesion.