Screening for prostate cancer with a blood test called PSA (prostate specific antigen) has been scrutinized due to limitations of the test, being not specific to prostate cancer and due to possible over-diagnosis of cancer. Urologists have addressed the shortcomings of PSA by smarter screening and using new tests to help decide whom to biopsy. MRI (Magnetic resonance imaging) is emerging as another tool to help in diagnosing and possibly screening patients.
Random 12-core biopsy is currently the gold standard procedure to diagnose prostate cancer. It is a brief office-based procedure done under local anesthesia whereby an ultrasound probe is inserted in the rectum and random biopsies are obtained from the right and left lobe of the prostate. The biopsy samples a very small percentage of the prostate and so it can be associated with false negative results.
Research has been undertaken to help improve selection of patients who need a biopsy. Imaging of the prostate has been a subject of interest for many years and especially multi-parametric MRI of the prostate. Recent improvements have helped better image the prostate to localize areas of concern. That requires special software that evaluates different characteristics of the prostate tissue. Lesions in the prostate are labeled as PIRADS 1 to 5 (prostate imaging-reporting and data systems), with PIRADS 1 and 2 likely showing benign lesions while PIRADS 3 being borderline and 4 and 5 being more concerning for cancerous tissue. New technology helps fuse the images of the MRI with the ultrasound so the urologist can accurately aim the biopsy needle to the lesion of concern.
Prostate cancer can be low risk (Gleason grade 3+3) or intermediate risk (Gleason grade 3+4 or 4+3) or high risk (Gleason grade 4+4 or higher). Clinically significant cancers includes intermediate and high-risk cancers. Studies have shown that MRI can help diagnose clinically significant cancers while limiting the detection of insignificant cancers. One can argue that this will help avoid over diagnosis of clinically insignificant (non-fatal) cancers.
MRI has been proven helpful in the setting of a rising PSA despite a negative random biopsy and this has become common practice nationwide. Another potential application of prostate MRI is to help select patients with low risk disease who would be good candidates for active surveillance. Patients that do go on active surveillance currently undergo surveillance random biopsies. These patients can potentially be followed up with MRI and MRI guided biopsies, thus reducing the number of biopsies. Studies to evaluate the utility of MRI in this setting are ongoing.
MRI however has its limitations. It can still miss up to 16 percent of clinically significant cancers and so a negative MRI should not mean that a random biopsy is not needed.
The addition of other tests like PSA density (PSA as it relates to the volume of the prostate) can help avoid missing these cancers and so further studies are needed. The decision to do a biopsy can potentially be based on a screening PSA and MRI. This will decrease the morbidity of having a random biopsy as well as avoid over diagnosis of clinically insignificant cancers. We are not there yet, but as always research is ongoing.