UPDATE - Issue 40 - Spring 2010
Improving the diagnostic pathway for men at risk of prostate cancer
by Hashim U Ahmed and Mark Emberton
The diagnostic pathway for men that are thought to be at risk of prostate cancer has remained the same since the discovery of PSA. The trouble with this pathway is that it is dependent on a series of tests that are not as good as we would like them to be. The performance of PSA is made worse by coupling it with another test – prostate biopsy – that is equally poor at doing the things that we want it to do.
The problem with prostate biopsy is that, as a test, it is not great at reassuring a man that he has no cancer – the so called 'false negative'. In contrast, when a prostate cancer is picked up on the biopsies, we cannot be very accurate about whether the cancer is a life threatening one or not, unless it contains features that we normally associate with aggressive disease (the so called ‘tigers’). Fortunately most biopsies that are positive do not contain these elements.
TRUS guided biopsies are inaccurate because they are carried out ‘blind’. The operator can see the prostate but not the cancer. This ‘blind’ approach is unique to the prostate. In other cancers, we can either see the cancer (say through a colonoscope) or we image it (just like in mammography for breast cancer).
If you picture the process it is easy to see just how cancers might be missed completely or skim the edge of a larger cancer and give the appearances of a smaller, less aggressive cancer (the apparent ‘pussycat’). These two errors lead to either the man being falsely reassured that he has no cancer or told that the actual amount or grade of cancer is less than it is.
We could offer a
test that would help
identify those men
who could safely
avoid a biopsy
For once we think that there may be a solution to this problem. Two novel imaging technologies show promise in detecting prostate cancer. These technologies are a new form of ultrasound (called tissue characterisation) and a state of the art magnetic resonance imaging (MRI scan, called multi-functional MRI). MRI uses magnetic pulses, and no radiation, to scan tissue. There exists preliminary data to show that both these tests are pretty good at ruling in and ruling out clinically important prostate cancer. If the former is true we could do targeted biopsies, as we do in all other cancers. If the latter is true we could offer a test that would help identify those men who could safely avoid a biopsy.
Prostate UK has been instrumental in assisting us to develop these ideas and to turn them into early studies. These data have allowed us to put together a grant application to the National Clinical Research Institute (Health Technology Assessment Programme) that has been successful. This £3 million grant will enable us to see whether MRI or indeed ultrasound can achieve the goal of fewer biopsies in men that do not need them and better biopsies in those that do.
We anticipate that this important study will start recruiting men in the autumn.