The PSA (prostate specific antigen) blood test is now widely acknowledged as an imperfect screening tool for prostate cancer (PCa). Because the test is not specific only for PCa but can indicate a variety of other noncancerous conditions, the decision about the next best step after an elevated PSA value is troublesome. Unless there is good reason to immediately do a transrectal ultrasound (TRUS) guided biopsy, many men are told to do one of the following:
- Wait for three months and do another blood draw (this rules our lab error or other test anomaly)
- Take a course of antibiotics to rule out infection as the source of a rise in PSA.
Even when patients are quickly referred for a TRUS biopsy, there is roughly one chance out of three that significant PCa will be missed or underdiagnosed.
Two recently published papers suggest that obtaining an MRI of the prostate is a preferred follow-up after a suspicious PSA result. De Visschere et al. (2016)[i] suggest that multiparametric MRI (T2-weighted, diffusion weighted, dynamic contrast enhanced and spectroscopy) may “reduce the risk of overdetection of non-significant PC and improve the early detection of clinically significant PC.” They point out that for men with repeat negative biopsies, mpMRI is being used more often to assist with an informed decision as to whether yet another biopsy is needed. They raise the question of whether responding to an elevated PSA by going directly to mpMRI might either eliminate the need for an initial biopsy if no significant PCa is detected; if so, this could qualify the patient for active surveillance. On the other hand, if the mpMRI picks up one or more significant lesions, an MRI-guided targeted biopsy can provide a more accurate diagnosis using fewer needles. Using MRI as an adjunct to a suspicious PSA result adds information needed to define next steps.
This proposal is reinforced by data from a study by Bergdahl et al (2015)[ii]. Based on the cases of 384 men who were screened as part of the Göteborg Randomised Screening Trial, they identified 124 men whose PSA was greater than 1.8 ng/ml and who then had an MRI before a biopsy. Those with a suspicious MRI and/or PSA greater than or equal to 3.0 ng/ml were referred for biopsy. Standard systematic (TRUS) biopsy blinded to MRI results was performed on those who met these criteria. In addition, targeted biopsy into the MRI-suspicious areas was performed on those whose MRI showed such areas. Three screening strategies were then statistically analyzed and compared:
- PSA > 3.0 + systematic TRUS biopsy
- PSA > 3.0 + MRI + targeted biopsy
- PSA > 1.8 + MRI + targeted biopsy
Twenty-eight cases of PCa were detected; 20 of them were in men who had no previous biopsies. The two strategies using MRI rather than TRUS biopsy were significantly here in both sensitivity and specificity than TRUS biopsy. Both MRI strategies detected more cases of significant PCa, while the TRUS method detected more insignificant PCa. The authors concluded, “A screening strategy with a lowered PSA cut-off followed by [targeted biopsy] in MRI-positive men seems to increase the detection of significant cancers while improving specificity.” Despite the relatively small sample, which the authors acknowledge as a limitation of the work, the statistics reinforce the concept that mpMRI has a valuable role to play between PSA test and prostate biopsy. This allows better decision making both for deferring treatment (Active Surveillance for those with insignificant PCa) and for identifying an immediate need for a targeted biopsy.
[i] De Visschere PJ, Briganti A, Fütterer JJ, Ghadjar P et al. Role of multiparametric magnetic resonance imaging in early detection of prostate cancer. Insights Imaging. 2016 Feb 4. [Epub ahead of print]
[ii] Bergdahl AG, Wilderäng U, Aus G, Carlsson S et al. Role of Magnetic Resonance Imaging in Prostate Cancer Screening: A Pilot Study Within the Göteborg Randomised Screening Trial. Eur Urol. 2015 Dec 24. pii: S0302-2838(15)01214-2. doi: 10.1016/j.eururo.2015.12.006. [Epub ahead of print]