March 2018, Dr Chee L Khoo
Patients and their GPs often agonise over elevated PSAs. Now, let’s not argue about whether we should or should not screen for prostate cancer. That was very last year. No matter what the RACGP or the urologists recommend we do, prostate cancer screening is still happening. Many but not all elevated PSAs end up with a trans-urethral ultrasound (TRUS) biopsy. Of course, not all elevated PSAs are prostate cancers. Nor are rising PSA levels.
TRUSB is not without significant morbidity including life threatening sepsis, though. It has limited sensitivity and has been criticised for over detection of insignificant cancer in one third of cases. If only, there is some other investigations that could help triage the elevated PSAs.
What about MRI prostate which is increasingly being used prior to TRUSB? Before we jump in, we must address a few very important issues:
- How sensitive is MRI of the prostate?
- How specific is MRI of the prostate?
- Does pre-operative MRI reduce unnecessary TRUSB?
- Can we utilise MRI of the prostate to screen men at high risk of prostate cancer?
Before we embark on any investigation, we need to know the test’s sensitivity and specificity. MRI prostate is relatively new and it has been a learning curve for all as one correlate radiological findings with operative findings. What does the evidence tell us?
PROMIS is a multicentre, paired-cohort, confirmatory study to test diagnostic accuracy of multi-parametric MRI (MP-MRI) and TRUS-biopsy against a reference test, template prostate mapping biopsy [TPM-biopsy]). Men with PSA up to 15 ng/mL, with no previous biopsy, underwent MP-MRI followed by both TRUS-biopsy and TPM-biopsy. The reporting of each test was done blind to the other tests.
They aimed to investigate whether MP-MRI could discriminate between men with and without clinically significant prostate cancer based on template prostate mapping biopsy (TPM-biopsy) as a reference test.
PROMIS also aimed to compare the accuracy of MP-MRI with that of TRUS-biopsy. They hypothesised that MP-MRI could be used as a triage test to decide which men with an elevated PSA might safely avoid immediate biopsy.9
There have been a number of studies exploring those numbers but they suffer from being single centre studies, retrospective in their analysis, non-blinding of imaging findings or non-standardised reference protocol. Some use TRUSB, some used TPM-Biopsy, used TPM-Biopsy with lesser number of biopsy while other used both.
In a recent Australian study from St Vincent’s Hospital, 150 men with an abnormal PSA or DRE underwent MP-MRI and template directed core biopsy as well MRI directed additional biopsies.
For significant cancer, sensitivity was 93-96%, specificity was 47-53%, and negative and positive predictive values were 92-96% and 43-57%, respectively.
Two systematic reviews declared sensitivities of between 58-96% with negative predictive value of 63-98% and specificity 23-78%. Large ranges indeed because of the differences in the studies.
PROMIS is the first study that presents blinded data on the diagnostic accuracy of both MP-MRI and TRUS-biopsy against an accurate reference test in biopsy-naive men with a suspicion of prostate cancer. It is the largest registered trial to date of the population at risk, across many centres and in which the conduct and reporting of each test was standardised and done blind to the other test results.
PROMIS concluded:
Sensitivity – 93% (in other words, if your MRI is negative, you will be right 93% of the time)
Specificity – 41% (in other words, if your MRI suggest that you MAY have cancer, you will be right 41% of the time)
In other words, the MRI is very useful to rule out cancer of the prostate and will significantly reduce the need for invasive prostate biopsy.
(This article first came out on sswgpl.com.au in February 2017)
Reference:
El-Shater Bosaily, A, Arya, M, Punwani, S et al. Re: Multiparametric magnetic resonance imaging guided diagnostic biopsy detects significant prostate cancer and could reduce unnecessary biopsies and over detection: a prospective study. J Urol. 2014; 192: 67–74
Futterer JJ, Briganti A, De Visschere P, et al. Can clinically significant prostate cancer be detected with multiparametric magnetic resonance imaging? A systematic review of the literature. Eur Urol 2015; 68: 1045–53.
Hashim U Ahmed*, Ahmed El-Shater Bosaily*, Louise C Brown*, Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. Lancet Jan 19 2017; DOI: http://dx.doi.org/10.1016/S0140-6736(16)32401-1