What's new in cancer: Prostate screening

Prostate cancer is the most common cancer amongst males in the UK, and the second most common cause of cancer-related death. (1) This could be attributed to lower levels of diagnostic testing. (2) There is evidence to suggest that organised national screening for prostate cancer can reduce mortality. (3)

However, there is currently no national UK screening programme for prostate cancer as until now, there has been no test reliable enough to detect prostate cancer that requires treatment at an early stage. The most investigated pathway is the prostate specific antigen (PSA) blood test for triage followed by prostate biopsy for verification. However, although a raised PSA level can indicate prostate cancer, it can also be elevated in other conditions that are not cancerous resulting in unnecessary and potentially painful biopsies for no reason. Conversely, around 1 in 7 of those with a normal PSA reading can still have prostate cancer, (4) so cases can be missed.

Furthermore, some types of prostate cancer detected by elevated PSA levels can be slow-growing and may never cause symptoms or result in death, meaning some males can receive intensive treatment unnecessarily with potentially serious side-effects that can impact their long-term quality of life. It is this over-diagnosis and the burden of overtreatment that has been the most significant hurdle in implementing screening programmes for prostate cancer.

In those with raised PSA levels, there is now strong evidence supporting the use of MRI (5) both in terms of reducing the number of unnecessary biopsies and detection of low-risk cancers as well being able to pick up more clinically relevant disease than standard biopsies.

This was shown definitively by the landmark PROMIS trial in 2017. Reported in the mainstream media as ‘the biggest leap in diagnosing prostate cancer in decades’ (6), the UK-based study (7) compared the effectiveness of conventional biopsies with MRI scans in detecting prostate cancer in those with elevated PSA levels.

MRI picked up 93% of aggressive cancers compared to only 48% using standard biopsies, throwing open the exciting possibility of utilising MRI as a stand-alone, non-invasive screening tool for prostate cancer.

The ReIMAGINE study (8) was designed as a prospective single-centre study evaluating the feasibility of using MRI as a primary screening tool for prostate cancer. Males identified at random across eight London GP surgeries were invited to attend for a screening MRI and PSA. 2096 invitations were sent out with 457 males responding and 303 completing both tests. Of the latter, 48 had a positive screening MRI indicating there may be a prostate cancer.

Remarkably, 32 of these had lower PSA levels than the current screening threshold of 3ng/ml meaning they would not have been referred on for further investigation based on PSA alone. The study demonstrates the feasibility of an MRI-led approach to prostate cancer screening and suggests it could offer a more robust means of detecting serious cancers, with the added value of a low rate of over-diagnosis. Critically, however, it also exposed a potentially significant inequality with respect to ethnicity; Black men were least likely to respond to the screening invite, doing so at one fifth the rate of white men.

Given that we know Black men are twice as likely to develop prostate cancer than white men, and once diagnosed the likelihood of dying is twice as high, it is absolutely vital that any national screening programme includes dedicated strategies to target this high-risk group and encourage their attendance for testing.

Whilst the use of MRI as a prostate cancer screening tool offers great hope for the future, its use on such a large scale will put significant demand on radiological reporting. With the Royal College of Radiologists already predicting a severe shortfall of clinical radiologists of 40% within five years, (11) innovative alternative strategies are clearly needed.

Macmillan Cancer Support has recently invested over £350,000 in Lucida Medical’s pioneering new artificial intelligence platform Pi™, (12) an AI tool that has been trained to identify prostate cancer from MRI scans. This is the second investment from Macmillan’s Innovation Impact Investment Portfolio and it could not come at a more opportune and exciting time.

With preliminary data suggesting the technology has accuracy equivalent to that of expert radiologists, (13) when used in conjunction with new screening techniques, it has the potential to truly transform the diagnosis of prostate cancer, with the aim of supporting earlier detection, the avoidance of unnecessary investigations and ultimately saving lives.