A Randomized Clinical Trial Comparing the Efficacy of MRI Versus PSA for Prostate Cancer Screening: The MVP Study (MRI vs PSA)
In this open randomized controlled trial, we seek to study whether prostate cancer screening
using multiparametric prostate magnetic resonance imaging (mpMRI) improves the detection
rate of clinically-significant prostate cancer (defined as Gleason score ≥7 on prostate
biopsy) compared with prostate cancer screening using prostate-specific antigen (PSA).
The current paradigm of prostate cancer screening relies upon an initial PSA blood test,
with subsequent investigations driven by the serum PSA level. This model has proven highly
controversial due to the inability of PSA level to discern between indolent and aggressive
forms of prostate cancer. As a result, numerous government-sponsored bodies have recommended
against PSA screening. Evidence suggests that prostate cancer screening has led to an
increased proportion of men being diagnosed with potentially curable prostate cancer.
However, due to the inability of the PSA level to accurately distinguish patients with
indolent and lethal forms of prostate cancer, it has led to a significant rate of
over-diagnosis of indolent disease. Magnetic resonance imaging has been gaining an
increasingly large role in the management of patients with clinically-localized prostate
cancer including diagnosis in patients with abnormal PSA levels, monitoring of patients on
active surveillance and staging prior to definitive interventions. MRI-based prostate cancer
risk assessment has been shown to better distinguish between clinically-significant and
insignificant tumours than PSA test. Therefore, a randomized controlled trial of MRI-based
prostate cancer screening and PSA-based prostate cancer screening is warranted.
- Clinically-significant prostate cancer
- Clinically-insignificant prostate cancer
BACKGROUND AND RATONALE:
Prostate cancer is the most common non-cutaneous malignancy and the third leading cause of
cancer death among men in Canada1. In 1987, prostate specific antigen was introduced for
prostate cancer screening2. Widespread adoption of PSA screening resulted in a significantly
increased number of incident cases and a significantly reduced number of cases of metastatic
disease at presentation3. Coinciding with the introduction of PSA testing, prostate cancer
mortality has decreased approximately 40% from an epidemiologic perspective4. Approximately
45-70% of the decline in mortality is attributable to PSA-based prostate cancer screening5.
Several studies have examined whether screening for prostate cancer using the PSA test
improves overall and prostate cancer mortality. In particular, two large randomized studies
in the U.S. and Europe have been conducted to evaluate this. Recently, the U.S. Preventative
Services Task Force (USPSTF) reviewed these and all studies to evaluate whether PSA should
be used as a screening test.
Current Recommendations for PSA Screening from the USPSTF
The USPSTF makes recommendations regarding the effectiveness of screening tests for
asymptomatic patients after assessing the evidence regarding benefits and harms of an
intervention. The most recent USPSTF guidelines regarding prostate cancer were published in
The first component of the USPSTF assessment is an evaluation of the benefits of early
detection and treatment of prostate cancer. The review panel drew on two large randomized
controlled trials which have been conducted to assess the effect of PSA-based prostate
cancer screening on prostate cancer mortality: the European Randomized Study of Screening
for Prostate Cancer (ERSPC)7 and the U.S.-based Prostate, Lung, Colorectal and Ovarian
(PLCO) Cancer Screening Trial8. In their recommendation the guideline panel do not consider
significant differences between the trials, in large part due to the fact that PSA had been
widely adopted in the US during the study interval while it did not have such uptake in
Europe. As a result, there are concerns that the trial did not compare screening to no
screening and that the trial would be unlikely to find a benefit even if a significant one
existed9. Regardless, the panel concluded that prostate cancer screening resulted in the
avoidance of 0 to 1 prostate cancer deaths per 1000 men screened6, a minimal benefit.
The second component of the guideline panel's assessment focused on potential harms of early
detection and treatment. They found evidence of significant harm due to false-positive PSA
results which confer a risk of psychological harm in addition to medical evaluation
including biopsy6. Further, they considered there to be, at minimum, a small harm associated
with prostate biopsy due to pain, bleeding and infectious risk. The panel also concluded
that there was significant evidence of at least moderate overdiagnosis and resultant
overtreatment among patients undergoing PSA-based screening.
Due to a perceived lack of benefit and presence of significant harms, the USPSTF concluded,
with moderate certainty, that the benefit of PSA-based screening did not outweigh the harms
and thus recommended against PSA-based screening for prostate cancer6.
A major limitation of this task force was that they received no input from experts in
prostate cancer in order to minimize bias. While this may improve the objectivity of the
review, many aspects of understanding prostate cancer were lost. In response to these
recommendations, the American Society of Clinical Oncology (ASCO) - the largest oncology
association in North America, developed a consensus statement to address the USPSTF
ASCO Provisional Clinical Opinion in Prostate Cancer Screening
The ASCO provisional clinical opinion on prostate cancer screening using PSA-testing was
based on an Agency for Healthcare Research and Quality systematic review10. Despite drawing
on the same data as the USPSTF, this panel concluded that men with a longer life expectancy
(greater than 10 years) may benefit from prostate cancer screening using PSA-testing11. In
men with a shorter life expectancy, PSA testing was discouraged. Unlike the USPSTF, the ASCO
panel placed greater weight on the results of the ERSPC, demonstrating a significant
reduction in the risk of prostate cancer death for men undergoing prostate cancer screening.
They noted similar harms as the USPSTF, namely false-positive results and prostate biopsy
Since the publication of this opinion, further data has become available which indicates
that the relative reduction in prostate cancer death from PSA-based screening may be larger
than previously estimated. The most mature data from the ERSPC has 13 years of follow up12.
Based on these data, the absolute risk reduction in prostate cancer mortality from PSA
screening was 0.11 per 1000 person years or 1.28 per 1000 men randomized. This risk
reduction has increased with increasing duration of follow up. Additional analysis has shown
an absolute risk reduction of metastatic disease was 3.1 per 1000 men randomized13. In a
subgroup of the ERSPC with longer follow-up, the absolute risk reduction in prostate cancer
mortality was 4.0 per 1000 men randomized14. This corresponds to a number needed to screen
of 293 and number needed to diagnose of 12 in order to prevent one prostate cancer death.
Underdiagnosis of Prostate Cancer with PSA
In addition to harms of biopsy and intervention, the primary concern regarding PSA-based
prostate cancer screening is the inability to distinguish between patients with indolent and
aggressive forms of the disease. Prostate cancer screening programs have traditionally used
a serum PSA cut-off of 4.0 ng/mL to indicate abnormality. However, many men with PSA values
in excess of 4.0 ng/mL do not have prostate cancer, and even fewer have clinically
significant prostate cancer. Further, up to 25% of men with PSA levels less than 4.0 ng/mL
will be found to have high-grade prostate cancer, if subject to biopsy15. Thus PSA-based
prostate cancer screening lacks both sensitivity and specificity to identify men with
aggressive prostate cancer. As a result, in addition to significant overdiagnosis and
overtreatment which has been well recognized, there is a risk for underdiagnosis.
Due to the USPSTF recommendations against PSA-based prostate cancer screening, there has
been a significant decrease in PSA testing being performed by primary care physicians16. It
is predicted that complete discontinuation of PSA-based screening would result in the
prevention of overdiagnosis for 710,000 to 1,120,000 men in the United States over a 12 year
period17. However, it would result in 36,000 to 57,000 preventable deaths due to prostate
cancer over the same time period. Thus, improved methods for prostate cancer screening may
allow for a diminishment in overdiagnosis while avoiding preventable deaths from prostate
Magnetic Resonance Imaging (MRI) of The Prostate
Multiparametric prostate magnetic resonance imaging (mpMRI) has an increasingly large role
in the management of patients with clinically-localized prostate cancer. MpMRI was initially
used as a staging test in patients with prostate cancer18. Despite the use of what would now
be considered obsolete technologies, Bezzi et al. demonstrated in 1988 that MRI could
identify nodal metastases with an accuracy of 88% and could distinguish disease localized to
the prostate from that invading beyond the capsule with an accuracy of 78% among patients
undergoing prostatectomy18. Since that time, there has been a migration in the use of MRI
earlier in the disease process.
In the realm of prostate cancer treatment, MRI is used for the monitoring of patients on
active surveillance following a prostate cancer diagnosis as a means of reducing prostate
biopsies, with their incumbent risks19,20. When performed in the evaluation of patients with
elevated PSA levels with previous negative prostate biopsy, mpMRI has been shown to identify
clinically significant prostate cancers which would have been otherwise missed by routine
systematic biopsy21. The use of MRI and ultrasound fusion imaging in the targeting of
prostate biopsy has increased detection of clinically significant prostate cancer while
limiting the diagnosis of clinically insignificant prostate cancer22.
Among men with an abnormal PSA who have never undergone a prostate biopsy, mpMRI
demonstrated promise in both the detection and exclusion of prostate cancer, using an
extensive prostate mapping biopsy (median 41 cores) as the referent23: the AUC was 0.27 (95%
CI 0.65-0.79). In a multivariable analysis of an independent cohort including age, family
history, prior 5-alpha reductase inhibitor use, digital rectal examination findings, PSA
level, PSA density, and MRI score, only MRI score was predictive of clinically significant
(Gleason score ≥7) prostate cancer among men without a history of previous prostate biopsy
(adjusted OR 40.2, p=0.01)24.
While historically prostate MRI has required the use of an endorectal coil25, recent
advances in MRI technology have obviated the need for the coil26, thus reducing the cost and
burden of the imaging.
Pilot Study to Examining the Feasibility of MRI Prostate Cancer Screening
We recently conducted a pilot study assessing the feasibility of mpMRI as an initial
prostate cancer screening test27. Following a newspaper based call for volunteers, we had
319 men present for possible inclusion in this study. Of these, 120 were eligible, 50 were
enrolled due to limitations in funding, and 47 completed the study protocol. Serum PSA
testing, mpMRI, digital rectal examination, and systematic (+/- targeted) prostate biopsies
were performed on all men.
Prostate cancer was identified in 18 of 47 men (38.3%). MpMRI (AUC 0.81, 95% CI 0.67-0.94)
significantly outperformed PSA (AUC 0.67, 95% CI 0.52-0.84) in the prediction of prostate
cancer. In multivariable analyses including age, digital rectal examination findings, PSA
and MRI score, mpMRI was the only significant predictor for the presence of prostate cancer
(adjusted OR 2.7, 95% CI 1.4-5.4). These findings persisted when we sought to predict only
clinically significant prostate cancer (Gleason ≥7; adjusted OR 3.5, 95% CI 1.5-8.3).
To better evaluate the use of mpMRI in prostate, a large, randomized study comparing the
efficacy of mpMRI in diagnosing clinically significant, aggressive prostate cancer, compared
to conventional PSA screening will be required.
View this trial on ClinicalTrials.gov