This commentary from JAMA give a good summary of where we are with 5 ARs ( Five alpha reductase inhibitors) and prostate cancers.Large randomized clinical trials (PCPT trial and the REDUCE trial have been done with finasteride (Proscar) and dutasteride (Avodart).
My take is that the 5 ARs seem to reduce the risk of developing low grade prostate cancer but may increase the risk of higher grade prostate cancer. However, a reasonable argument can be made that the 5 ARs do not in fact increase the risk of high grade cancer but just make the cancers more easily detectable but we probably will never know because is is unlikely that many further studies will be done and I doubt further analysis of existing data will be convincing.
One can also argue that a 5 AR driven decrease in the occurrence of low grade prostate cancer may not translate into fewer prostate cancer deaths. Most every diagnostic or therapeutic decision involves a tradeoff, but here exactly what the tradeoff here is remains unclear.The drugs clearly decrease prostate size but in regard to prostate cancer there is much lingering doubt.
As hard as answers are to come by in preventive medicine issues ( think the changing panorama of suggestions for healthy diets and aspirin use, glucose control in diabetics, etc), it is astounding that the population medicine folks think that they can discern what preventive measures "should" be done and would be willing to recommend that some should have to forgo treatment so some in the future would be the beneficiary of some greater aggregate good. See here for Dr. Harold Sox's plan for just that policy.Hubris-city.
I used to spend considerable time giving preventive medicine advice in the context of a corporate wellness program. As I think back on what I said then ( with more certainty that the data warranted ) I have more than a few doubts now about what I said then. The only thing I am more sure about now is that for the most part regular exercise is a good thing. I am much less sure about the advice I gave about aspirin and statins for primary coronary disease prevention and for PSA screening and screening for bone density. It may well be that randomized clinical trials are the best we can do in terms of discerning medical management plans but it not uncommon to do RCTs and still the answer(s) remain undetermined as is the case of the reductase inhibitors.
The old plaintiff lawyer meme of "Doctor, were you wrong then or are you wrong now" continues to hit home, particularly in the enterprise of preventive medicine.