Prostate cancer screening: long-term results
Screening does prevent deaths from prostate cancer. But the harms it can cause by diagnosing too many cancers mean it should not be introduced yet, researchers say.
BMJ Group News
What do we know already?
For many years we have known that a blood test for raised levels of a substance called prostate specific antigen (PSA) can help doctors diagnose men with prostate cancer. (The prostate is a gland at the base of the penis.) But there are two main problems with the PSA test. Firstly, it is not very accurate. Secondly, it spots many low-risk prostate cancers that don’t grow or cause any problems during the man’s lifetime. This is known as over-diagnosis. This means more men have prostate cancer treatment than actually need it. This is known as over-treatment. Prostate cancer treatments can cause erection problems and bladder problems.
In England men can request a PSA test, although it is not automatically offered to all men. There have been many studies looking at whether the benefits of PSA testing outweigh the chances of being harmed by over-diagnosis and over-treatment. But the results haven’t been clear. Because of this, PSA testing is controversial.
How was the new study done?
This study was set up in 1993 and includes men in eight European countries. More than 162,000 men were randomly chosen to have either regular PSA testing (every four years, or two years in Sweden) or no testing. The authors of the study have already published the results after the first nine and 11 years. This study includes the results 13 years after the men were put into their groups. The main result the researchers were interested in was how many men died of prostate cancer in the two groups.
What does the new study say?
Men who were chosen to have PSA tests were less likely to have died of prostate cancer after 13 years. The researchers calculated that there was one fewer death from prostate cancer for every 1,000 men in the study. And they calculated that they needed to invite 781 men for a PSA test to prevent one man from dying from prostate cancer.
Not surprisingly, more men who had PSA tests were diagnosed with prostate cancer. Most of the cancers (60 in every 100) detected by PSA testing turned out to be low-risk when doctors checked them using a test called a biopsy. The researchers calculated that one man was prevented from dying from prostate cancer for every 27 extra cancers that were detected by PSA testing.
How reliable is the research?
This was a big, well-organised study and the overall results are likely to be quite reliable. However, there are two problems. There was quite a big difference between the results in different countries, more than you would expect from differences in how prostate cancer is treated. These unexplained differences might have affected how reliable the results are.
Another problem is that quite a lot of men who were in the no-testing group actually did have PSA tests at some stage, outside of the study. This would usually mean the results underestimated how much difference the test made.