MRI has improved the way prostate cancer is diagnosed. Many men now have an MRI scan before their biopsy to detect prostate cancer. MRI can be used to do a targeted biopsy, where the biopsy needles aim for the area where tumours appear on the scan. There has been much debate over whether targeted biopsies can replace the older, systematic biopsy technique. The MRI-FIRST study has compared the two biopsy techniques head-to-head, showing that men would benefit from both types of biopsy for prostate cancer diagnosis.
Multiparametric MRI detection of prostate tumours prior to biopsy
Multiparametric MRI (mpMRI) is a very sensitive scanning technique that can be used to detect prostate tumours. MRI scans don’t use x-rays, like CT scans. They use strong magnetic fields and radio-waves to generate an image of the body. They can be used without the fear of damage from radiation. Unfortunately, an MRI can’t be used for people who have some types of metal implant. These may include pacemakers, piercings, artificial heart valves, surgically-implanted joints and many others. During an MRI scan, the person is moved inside a tunnel in the MRI machine. This can be stressful for people uncomfortable with being in enclosed spaces. The scan is also very noisy.
MRI is particularly useful in finding aggressive tumours, these being Gleason grade group 2 and above (Gleason 3+4=7 and above). These tumours are often referred to as “clinically significant prostate cancers”.
Prostate cancer diagnosis in Australia is done by biopsy, with an MRI commonly used beforehand. During the biopsy procedure, fine needles are inserted into the prostate gland and small samples of prostate tissue are removed for laboratory analysis. Biopsy is a much more invasive procedure than MRI. It often causes pain and bleeding, and comes with a risk of infection. But biopsy brings many benefits, such as an understanding of what type of cancer is present (i.e. adenocarcinoma or a different type) and the Gleason score to predict how fast it is growing.
Targeted and systemic biopsies
Having an MRI scan before a biopsy can change the way a biopsy is done. Since the scan shows where the tumours are in the prostate gland, this information can be used to target the biopsy needles towards the tumour.
Targeted biopsies use imaging to aim for visible tumours, rather than taking samples from many random regions. MRI-targeted biopsies are common in Australia. These use MRI information during the biopsy, to ensure the needles go into the tumour site.
The older biopsy method is called systematic biopsy. During this procedure, the biopsy needles go into random parts of the prostate, trying to cover all regions of the gland. Depending on the size of the prostate, this could mean 10 samples, or even up to 50 samples are taken.
Which is best, systematic or targeted biopsy?
There are pros and cons to both biopsy techniques. By taking many random samples from all over the prostate, systematic biopsies are more likely to pick up spots that are difficult to see on an MRI image. But if only a systematic biopsy is done, with no imaging, a small tumour could be missed by chance. A targeted biopsy can ensure that an obvious tumour is not missed by the biopsy needle.
Whether to use targeted or systematic biopsies has been a subject of research and debate for many years. It has also been discussed in a blog from 2017.
At least five randomised trials have addressed the question of which type of biopsy is best. But their results were contradictory. The PRECISION study, published last year, showed that the detection rate for “clinically significant” tumours (Gleason 7 and over) was higher for men who had mpMRI and targeted biopsy compared to men who had systematic biopsy only. This study involved two groups of men, who had either one or the other type of biopsy. Men who had a negative MRI in this study did not go on to have a biopsy.
The PRECISION and PROMIS trials have been useful in defining good protocols for diagnosis. But there is still an unanswered question here. Can having an MRI before biopsy mean that a systemic biopsy is unnecessary, or does doing a systemic biopsy give us essential information that improves diagnosis? In other words – can we do away with the systemic biopsy? This was the question discussed in the 2017 biopsy blog. At the time, the case was made by Dr Guillaume Ploussard, that systematic and imaging-targeted biopsies are complementary techniques, and therefore should be used side-by-side. A new study has been published that supports this case.
MRI-FIRST study
The MRI-FIRST study is a diagnostic trial conducted in France. The first author of the publication is Prof Olivier Rouviere from the Hospices Civils de Lyon, France. The aim of this study was to perform systematic AND targeted biopsies for every patient, to determine whether the systematic biopsy was worth doing.
275 men with localised prostate cancer joined the study, from 16 different medical centres over France. They had PSA levels of 20 ng/ml or less. Each man had an MRI scan, then a systematic biopsy, then a targeted biopsy. The radiologist performing the systematic biopsy had not seen the results from the MRI. Prostate cancer of Gleason 7 and above was detected in 94 of these men.
Of the 94 men who were diagnosed with prostate cancer in the study, 14% were diagnosed by systematic biopsy only, 20% by targeted biopsy only, and 66% of men were diagnosed by both techniques.
So the systematic biopsy missed some cases of prostate cancer, but so did the targeted biopsy. The researchers calculated that clinically significant prostate cancer would have been missed in 5.2% of cases if the systematic biopsy had not been done, and in 7.6% of cases if the targeted biopsy had not been done. These numbers were not considered significantly different by statistical tests. In other words, the results of the study did not provide enough evidence to conclude that either technique was superior.
What these results did show, is that detection of clinically significant prostate cancer was improved by using both types of biopsy. The researchers concluded that obtaining an MRI before biopsy improved the detection of clinically significant prostate cancer, but did not seem to avoid the need for systematic biopsy.
One problem with this approach is that adding the systematic biopsy to the targeted biopsy increased the detection of small, slow-growing tumours. This could lead to over-diagnosis and over-treatment of prostate cancer, that is not considered clinically significant.
Results from the MRI-FIRST study have made a very important contribution to the debate over which biopsy technique is best. It will be interesting to see how this new information affects biopsies in the future. For now, this study has reinforced the value of the systematic biopsy, supporting the case made by Dr Ploussard in 2017.
