Multiparametric MRI for Prostate Cancer - 062
Multiparametric magnetic resonance imaging (mpMRI) is a special type of scan that combines several different imaging techniques to create detailed pictures of your prostate. It gives your healthcare provider both structural and functional information about your prostate.
This post mainly focuses on using mpMRI in prostate cancer detection and active surveillance.
Unlike regular MRIs, which take standard pictures, mpMRI uses multiple "parameters" or types of scans to gather more information.
T1 and T2-weighted imaging show anatomy.
Diffusion-weighted imaging shows how densely packed cells are.
Dynamic contrast-enhanced imaging shows blood flow patterns.
These combined views help doctors identify suspicious areas that might contain cancer. The primary goal is to detect clinically significant prostate cancer, which is generally defined as Grade Group 2 (Gleason score 3+4=7) or higher, often with a tumor volume ≥0.5 mL or evidence of extraprostatic extension (EPE).
Importantly, mpMRI uses magnetic fields rather than radiation, so it doesn't increase the risk of developing other types of cancers.
When Is Multiparametric MRI Appropriate
The National Comprehensive Cancer Network (NCCN) and the American Urological Association (AUA) guidelines recommend mpMRI in several situations:
If you have an elevated PSA level but a previous negative biopsy.
Before a first prostate biopsy, to better target suspicious areas.
For active surveillance of men with low-risk and favorable intermediate-risk prostate cancer.
When deciding if you need a repeat biopsy.
If your doctor suspects prostate cancer despite a normal or low PSA level.
Details from the guidelines
The AUA's 2023 guidelines on early prostate cancer detection say that clinicians may use mpMRI before an initial prostate biopsy to improve the detection of clinically significant cancer, more aggressive cancers that truly need treatment.
If the mpMRI shows something suspicious, the AUA recommends a targeted biopsy of that area, typically combined with a systematic biopsy. A systematic biopsy uses ultrasound guidance to sample the prostate in a grid-like pattern taking 10 to 12 cores from both lobes of the gland.
Combining mpMRI-targeted and systematic biopsies increases the detection of clinically significant cancer while reducing the chance of missing tumors not visualized by the MRI.
Suppose the mpMRI looks normal, but there are other signs that the risk is still high, such as a persistently high PSA or high PSA density. In that case, the guidelines advise not to rely on MRI alone, but recommend considering a systematic biopsy despite a normal mpMRI.
PSA density is calculated by dividing the PSA level by prostate volume as measured by MRI or transrectal ultrasound. The NCCN and AUA guidelines acknowledge that a PSA density >0.15 ng/mL/g suggests a higher cancer risk.
mpMRI may also be helpful for men who have had a prior negative biopsy but still have an elevated PSA or cancer suspicion. In such cases, the guidelines strongly recommend getting an mpMRI before doing another biopsy.
An mpMRI might show a lesion that the first biopsy missed. The AUA recommends an mpMRI for patients with a negative initial biopsy but ongoing suspicion. If the mpMRI shows a suspicious area, as indicated by a PI-RADS score of 3–5, a doctor can perform an mpMRI-targeted repeat biopsy.
This approach can yield clinically significant prostate cancer by avoiding another blind sampling of the prostate.
An abnormal digital rectal exam (DRE), like a lump, irregularity, or firmness felt on the prostate, is another trigger for an mpMRI in many cases. NCCN's early detection guidelines highlight the role of mpMRI, particularly for men with an elevated PSA or an abnormal DRE.
If your doctor recommends an mpMRI, they should discuss why with you. This could be to avoid an unnecessary procedure or ensure a biopsy is as accurate as possible.
Overall, an mpMRI is about personalizing prostate cancer screening. It helps zero in on clinically significant tumors and gives more peace of mind when results are normal.
Understanding the PI-RADS Reporting System
After your mpMRI, a radiologist will use the Prostate Imaging-Reporting and Data System (PI-RADS) to score any suspicious areas. This standardized 5-point scale helps doctors understand how likely an area is to contain clinically significant cancer.
The radiologist examines the multiple MRI sequences and gives each lesion a score from 1 to 5. The higher the score, the more likely that area is a clinically significant cancer, meaning a cancer that would likely need treatment.
Your doctor will use the PI-RADS score and other factors like your PSA level, PSA density, age, family history, and prior biopsy results to decide the next steps. In general:
PI-RADS 4 or 5 lesions are considered suspicious for clinically significant prostate cancer and usually warrant a targeted biopsy.
PI-RADS 1 or 2 lesions are considered unlikely to be cancer, and active monitoring may be appropriate, especially if other risk factors are low.
PI-RADS 3 is indeterminate and may lead to biopsy depending on additional risk factors like PSA density or prior biopsy history.
For example, your report might say, "PI-RADS 5 lesion in the left apex," which tells the urologist that there's a very suspicious area at a specific location worthy of targeted biopsy. Or it might say, "PI-RADS 1 – no abnormal lesions," which indicates that nothing on the MRI raises concerns.
Limitations of Multiparametric MRI
While mpMRI is a powerful tool, it’s not perfect:
Small tumors (less than 0.5 cm) may be missed.
Studies show mpMRI can miss 10–15% of clinically significant cancers, particularly in the anterior or transition zones or smaller-volume lesions.
Some aggressive cancers don’t form a clear mass or show restricted diffusion, making them hard to detect.
Scan quality depends on the equipment: 3T MRI is preferred over 1.5T.
Reader expertise matters: Interpretation can vary significantly between radiologists, especially for PI-RADS 3 lesions. Centers with experienced radiologists generally have higher diagnostic accuracy.
False positives are possible, especially with inflammation, prostatitis, or benign nodules, which may lead to unnecessary biopsies.
Not all men can undergo MRI, especially those with metal implants, severe claustrophobia, or advanced kidney disease.
Insurance coverage varies, and out-of-pocket costs can be high.
It's important to remember that a "normal" mpMRI doesn't completely rule out cancer. It just means the radiologist didn't see any suspicious areas on the scan.
Multiparametric MRI may miss certain cancers
The PROMIS study, published in The Lancet in 2017, looked at the diagnostic accuracy of mpMRI compared to transrectal ultrasound-guided biopsy for detecting prostate cancer in men with clinical suspicion, before any biopsy.
The PROMIS study had a primary definition for clinically significant cancer as:
Gleason score 4+3 = 7, OR
A maximum cancer core length of 6 mm (of any Gleason grade).
The PROMIS results indicated a Negative Predictive Value (NPV) of 89% for mpMRI for this primary definition. This means that 11% (1 in 9) of men with a negative MRI were found to have clinically significant cancer.
When the study used a broader definition of clinically significant cancer—a Gleason score of 3 + 4 = 7 or a maximum cancer core length of 4 mm—28 % (roughly 1 in 4) of men with a negative MRI had a clinically significant cancer.
This study is a good reason why the guidelines recommend considering all risk factors and possibly using liquid biomarkers when deciding to perform a prostate biopsy, and not just relying on mpMRI results.
Multiparametric MRI can be pretty reliable
Other studies are more promising.
A pooled review of 21 studies covering almost 4,000 men showed that multiparametric MRI (mpMRI) guided by PI-RADS scores has a sensitivity of about 89 % and a specificity of about 73 % for detecting prostate cancer. This study shows that mpMRI finds roughly nine out of ten clinically significant cancers while limiting false alarms.
Another study of 207 men undergoing active surveillance underwent MRI-ultrasound fusion biopsy with a concurrent systematic biopsy. 14% of the men experienced pathologic upgrading of their tumor that was otherwise undetected by systematic biopsy.
A study of 85 men who initially qualified for active surveillance underwent mpMRI with MRI/Ultrasound fusion-guided prostate confirmatory biopsy. Adding mpMRI resulted in 29% of the men no longer meeting criteria for active surveillance.
In another study, 281 men qualified for active surveillance based on systematic ultrasound-guided prostate biopsy. Subsequent mpMRI-targeted biopsy resulted in 10% of the men no longer being eligible for active surveillance.
Variability in Radiologist Interpretation
The accuracy of mpMRI results depends partly on who reads your scan. Studies have shown that interpretation can vary between radiologists due to:
Different levels of experience with prostate MRI.
Subjective judgment in assigning PI-RADS scores.
Variations in image quality between different MRI machines.
Different medical centers use different protocols.
This variability is why it's beneficial to have your mpMRI interpreted by a radiologist with special training and experience in prostate imaging. Some medical centers now have dedicated "prostate MRI experts" who interpret these scans.
Studies have shown that the accuracy of mpMRI interpretation improves with the radiologist's experience and specialized training. Prostate cancer centers of excellence have radiologists with this experience and training.
Combining mpMRI with Liquid Biomarkers for Better Accuracy
To improve screening accuracy and avoid unnecessary biopsies, doctors are increasingly using mpMRI with biomarkers, including tests called liquid biomarkers, which I discussed in a prior newsletter. This approach creates a more complete picture of your prostate health.
Biomarkers, including liquid biomarkers, used in conjunction with mpMRI include:
PSA density (PSA level divided by prostate volume measured on MRI)
Free-to-total PSA ratio
Prostate Health Index (PHI)
4Kscore test
SelectMDx
ExoDx urine tests
PCA3 urine test
When these tests are combined with mpMRI results, doctors can better determine who needs a biopsy. For example, if your mpMRI shows a PI-RADS 3 lesion (intermediate suspicion), biomarker tests help decide whether you should proceed to biopsy or continue monitoring.
NCCN guidelines support a more comprehensive approach to detecting prostate cancer. Instead of relying on a single test, this “multiparametric” strategy combines different types of information to give a more accurate picture of a man’s risk.
What This Means for You
If your doctor recommends an mpMRI, it's a valuable tool that can provide important information about your prostate health. The test is most helpful when used as part of a comprehensive approach to prostate cancer detection, considering your PSA history, other biomarkers, family history, and overall health.
By combining mpMRI with other tests, your doctor is taking an intelligent approach that aims to find significant cancers while avoiding unnecessary procedures. Always talk with your doctor about how the results of your mpMRI influence their decisions about your care.
NCCN Position Regarding mpMRI:
Recommends consideration before biopsy.
Strongly recommend before repeat biopsy.
Supports MRI-targeted fusion biopsy approach.
AUA Position Regarding mpMRI:
Acknowledges utility but takes a slightly more conservative stance.
Recommends consideration, particularly for men with prior negative biopsy.
Less prescriptive about routine pre-biopsy MRI for initial evaluation.
Questions to Ask Your Provider
What is my PSA density and PI-RADS score on my mpMRI, and what do they mean?
Would an mpMRI of my prostate be appropriate at this stage?
Would additional blood or urine biomarker tests, like PHI or 4Kscore, help clarify whether I need a biopsy?
Could imaging, such as an mpMRI, be combined with these biomarker tests to improve accuracy?
How much experience does the radiologist who read my prostate MRI have with these specific types of scans, and do they have any special qualifications for interpreting them?
Conclusion
As a physician who believes in patient empowerment, I encourage you to have meaningful conversations with your healthcare provider. Ask about your PSA density, PI-RADS score, and whether additional biomarker tests might help clarify your situation. Your prostate health journey should be personalized to your specific circumstances, risk factors, and concerns.
The future of prostate cancer detection and active surveillance lies not just in better technology but also in more innovative and individualized approaches that find dangerous cancers that need treatment while sparing men from unnecessary procedures.
mpMRI is an important step in that direction, but it still requires the skilled interpretation and judgment of experienced healthcare professionals.
Until the next newsletter, stay healthy.
Much love,
Keith
Thank you, Dr. Holden, for your informative articles. This was quite interesting and informative. Much appreciated.