The difficulty of modern medicine

We have countless diagnostic tests, but they aren't always that good at actually predicting disease progression. Take this new research on the PSA test for prostate cancer:

As many as two of every five men whose prostate cancer was caught through a PSA screening test have tumors too slow-growing to ever be a threat, says a new study that raises more questions about the controversial tests.

The work "reinforces the message that we are overdiagnosing prostate cancer," said Dr. Len Lichtenfeld of the American Cancer Society, who was not involved in the new study.

More than 186,000 U.S. men will be diagnosed with prostate cancer this year, and nearly 29,000 will die, according to cancer society estimates. Most men over 50 have had a blood test that measures prostate specific antigen, or PSA, mostly for routine screening.

There begins the list of problems: Most men who undergo a biopsy for an abnormal PSA test don't turn out to have prostate cancer; high PSAs often signal a benign enlarged prostate. Of those who do have cancer, there's no proof yet that early detection saves lives -- as most prostate tumors grow so slowly that had they not been screened, those men would have died of something else without the anxiety.

And then there was that study from Norway which suggests many breast cancers disappear on their own.