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Half of Prostate Cancers Found on MRI Missed by PSA Testing

Using MRI scans in screening for prostate cancer could detect tumours missed by prostate-specific antigen (PSA) blood testing alone, according to a major new study from University College London (UCL) and King's College London. 

The researchers noted that using either PSA or an abnormal digital rectal examination (DRE) to select men for a standard transrectal biopsy could reduce prostate cancer mortality at 16 years by 20%, but was associated with significant overdiagnosis and overtreatment of lower risk cancers.

Use of MRI Increased Cancer Detection and Reduced Unnecessary Biopsy

The recent introduction of MRI as a first step in investigating a raised PSA or abnormal DRE had been shown to increase detection of clinically significant cancers, while reducing overdiagnosis and sparing one in four high risk men from an unnecessary biopsy.

However, MRI as a screening tool had not been assessed independently of PSA in a formal screening study. So the researchers performed a systematic community-based assessment of the prevalence of prostate MRI lesions among men aged 50 to 75 from eight participating general practices who were invited for a prostate health check. The 2096 invitations sent garnered a 22% response rate, from among whom 303 men completed both MRI and PSA screening tests. 

The study, dubbed ' ReIMAGINE ' and published in BMJ Oncology, is the first to use MRI scans along with PSA density to assess the need for further investigation. Researchers reported that one in six men (48/303, 16%) had a positive screening MRI, of whom 32 had a PSA <3 ng/mL – the current benchmark for performing additional tests such as a biopsy. An additional one in 20 men (16/303, 5%) had a raised PSA density alone.

After NHS assessment, 29 men (9.6%) were diagnosed with clinically significant

cancer and 3 men (1%) with clinically insignificant cancer. Of the 29 men found to have serious prostate cancer, 15 of 25 with a positive MRI had a PSA score <3 ng/mL as did two in three men with a positive MRI. In other words, the team said, over half of the men with significant cancer on biopsy would not have been referred for further investigation under the current system.

In contrast, fewer than 1% of screened men were 'overdiagnosed' by MRI when they actually had low-risk disease.

MRI Could Also Have Value in Screening 

The researchers concluded that: "Prostate MRI may have value in screening independently of PSA." They noted that while currently men over 50 in the UK can ask for a PSA test, they "hoped that using MRI as a screening tool that is offered to men without them needing to ask for it could further reduce prostate cancer mortality and overtreatment".

Chief investigator Professor Caroline Moore from UCL's Department of Surgical and Interventional Science, and a consultant surgeon at UCLH, said: "The thought that over half of the men with clinically significant cancer had a PSA <3 ng/mL and would have been reassured that they didn't have cancer by a PSA test alone is a sobering one." 

Higher Mortality in UK Due to Less Testing

Senior author Mark Emberton, professor of interventional oncology at UCL, said: "The UK prostate cancer mortality rate is twice as high as in countries like the US or Spain because our levels of testing are much lower than other countries. Given how treatable prostate cancer is when caught early, I'm confident that a national screening programme will reduce the UK's prostate cancer mortality rate significantly. There is a lot of work to be done to get us to that point, but I believe this will be possible within the next 5 to 10 years."

Asked to comment by Medscape News UK, Alice Davies, health information manager at Cancer Research UK, which part-funded the research, explained that the reason there was currently no national screening programme for prostate cancer was because the PSA test wasn't reliable enough. Evidence showed that PSA testing in men without symptoms did not reduce prostate cancer mortality and caused some men to be treated for cancers that would not go on to cause harm in their lifetimes.

"This early-stage research shows the potential of using MRI scans alongside PSA as a screening tool for prostate cancer," Ms Davies said. "But further research is needed in a larger sample of men to determine how well the test performs and whether it would save lives from prostate cancer."

Trial Results "Extremely Exciting"

Also commenting to Medscape News UK, Simon Grieveson, assistant director of research at Prostate Cancer UK, said that when prostate cancer was caught early, it was very treatable. "Sadly, more than 10,000 men each year are diagnosed too late, when their cancer has already spread.  

He added: "MRI scans have revolutionised the way we diagnose prostate cancer, and it's great to see research into how we might use these scans even more effectively. These results are extremely exciting, and we now want to see much larger, UK-wide studies to understand if using MRI as the first step in getting tested could form the basis of a national screening programme." 

The investigation was supported by the National Institute for Health and Care Research UCLH Biomedical Research Centre, the Medical Research Council, and Cancer Research UK.

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