PSA screening for prostate cancer reduces deaths, but the benefit is smaller and slower to appear than many men might expect. A new review of six trials involving nearly 800,000 men found that about two fewer men died from prostate cancer for every 1,000 screened, a result that usually became clear only after very long follow-up.

That means roughly 500 men must be screened to prevent one death from prostate cancer, and the benefit in the European randomized study of screening for prostate cancer was only apparent after 23 years. The findings give fresh weight to an argument that has split doctors and policy makers for years: screening can save lives, but it can also lead men down a path of tests and treatments they may never have needed.

Prof. Philipp Dahm, one of the researchers behind the review, said prostate cancer screening does reduce prostate cancer mortality, but only after a very extended period of time to realise that benefit. He called the finding a milestone and said it would make a difference for many policymakers. Dr. Juan Franco, another researcher involved in the review, said the results are not a blanket endorsement of universal screening and warned that the tests come with very real risks.

Those risks matter because the PSA test can detect benign cancers that may never cause problems, yet the next step is often radiotherapy, surgery or hormone therapy. In the ProtecT trial, between 8% and 47% of men reported problems with urinary or sexual function after radiotherapy or surgery for prostate cancer. Incontinence and impotence are among the complications that can follow treatment, which is why screening remains controversial even when it appears to save lives.

The debate is especially relevant in Britain, where more than 64,000 prostate cancer cases are diagnosed every year and one in eight men will develop the disease in their lifetime. The risk rises to a quarter of Black men. Last year, the UK National Screening Committee advised against prostate cancer screening for most men, while recommending a targeted programme for men with BRCA1 and BRCA2 mutations.

The new review does not overturn that caution. It does, however, sharpen the choice facing health systems that have no formal screening programmes, including the UK and many other countries. Men at highest risk are still being considered for more focused screening, and researchers are studying newer approaches that use more prostate-related proteins in the blood and MRI scans. But the team said it is too early to know whether those methods will save more lives or cause less harm.

For now, the message is not that every man should be screened, but that prostate cancer screening can prevent deaths if enough men are followed long enough. The harder question for doctors and policy makers is how to capture that benefit without exposing large numbers of healthy men to unnecessary treatment.