One of my interests: screening for cancer among a healthy population may do more harm than good: needless anxiety and additional tests, all too often radical treatments applied as a preventive measure.
The PSA test may be a particularly good example, since prostate cancer is often slow growing, but I believe there is a similar controversy about breast cancer screening. I remember reading or seeing that some time ago diagnostic screening got far ahead of medical knowledge about cancer: doctors were seeing cancers on the screen that they just didn't recognize. Was it malignant or not? Fast-growing or not? A threat of any kind, even to a woman's quality of life, or not? If they don't have these answers, how has the screening done more good than harm?
Even in the case of searching for a gene mutation that makes breast cancer likely, there are trade-offs in doing the test, including false positives and (ironically) increased risk of cancer from the radiation.