“Build a better mousetrap and the world will beat a path to your door.” These famous words are from Ralph Waldo Emerson. As a philosopher, Emerson was the father of Transcendentalism, a lofty system of thought emphasizing self-reliance and a spiritual connection with nature. Thus, it seems surprising that he would offer such a such a practical, down-to-earth idea.

I think his advice applies to a key factor that is transforming the world of prostate cancer (PCa). Today’s technologies for detecting, diagnosing and treating PCa have been improved by better imaging. Doctors and patients alike are beating a path to imaging centers that offer multiparametric MRI (mpMRI) on powerful 3T magnets. While the dream of conquering PCa may be lofty, mpMRI is a practical, down-to-earth step toward achieving that goal.

Consider that mpMRI enables such advances as

• Image-based detection of a suspicious prostate tumor, thus clarifying a high or rising PSA
• Determining if a biopsy is necessary based on the PI-RADS score of the scan
• Real-time guidance of a minimum number of biopsy needles targeted to the core of the suspicious area, thus affording the greatest diagnostic accuracy with the least risk of biopsy side effects
• Real-time imaging guidance of focal therapies such as Focal Laser Ablation or TULSA for appropriate patients

These improvements have brought us to a new level of clinical services for PCa. Not only can we accurately match a treatment strategy to a patient’s disease, MRI guided focal treatments have enlarged the range of treatment choices. Since it’s never been this good, one might be tempted to think it can’t get better than this.

But then, there’s always a desire to “build a better mousetrap,” and so it is with imaging. Let’s take the example of MRI-guided targeted biopsy. A recent conference report states, “MRI is a well-established tool for prostate biopsy guidance, improving detection of clinically significant prostate cancer compared to systematic TRUS–guided biopsy. However, MRI has limitations, as it may miss smaller, less aggressive clinically significant prostate cancer that may potentially be identified by PSMA PET/CT.”

Although mpMRI excels at revealing prostate masses that are suspicious for clinically significant PCa—that is, cancer that should be biopsied and likely needs treatment—it does not pick up molecular differences that signal more dangerous cells. On the other hand, PSMA PET/CT uses radioisotopes (nuclear medicine) that are chemically structured to bond with cancer cells; these isotopes “light up” under CT imaging, revealing very small clusters of PCa cells. Currently, PSMA PET/CT is not routinely used for initial diagnosis, but rather for body scanning to look for PCa recurrence after treatment, or to detect suspected metastatic disease on initial diagnosis when a newly diagnosed patient has a PSA blood test greater than 100.

Thus, some researchers wonder if a combination of mpMRI + PSMA PET/CT would improve biopsy-proven diagnosis by revealing additional significant PCa not picked up my mpMRI alone. To test whether doing so would constitute a “better mousetrap” for more aggressive cells. A randomized trial was designed to compare MRI only-guided prostate biopsy vs. MRI + PSMA PET/CT-guided biopsy. 70 patients whose MRI showed at least one PI-RADS 4 lesion were enrolled. Half were randomly assigned to Arm 1 (MRI-only targeted plus 12-core biopsy), and half to Arm 2 (mpMRI + PSMA PET/CT-guided biopsy).

For Arm 2, experienced radiologists “fused” the MRI + PSMA PET/CT images to provide the biopsy guidance. The trial goals included accurate detection/diagnosis rates of clinically significant PCa, also all PCa (significant or not), between the two image guidance systems.

The results showed that in Arm 2 (combined imaging) the addition of PSMA PET/CT showed slightly better results for predicting which patients had clinically significant PCa, but the improvement was not statistically significant. In other words, the combination approach correctly identified slightly more specific lesions, but in fact the number of patients diagnoses in each group was roughly equivalent.

To me, this suggests that until further comparison studies are done with larger enrollment, I doubt that clinicals will beat a path to using combined mpMRI + PSMA PET/CT imaging for initial diagnosis—unless a patient has an unusually high PSA test. The expense of nuclear imaging in addition to MRI is likely to be prohibitive, not to mention the relative scarcity of centers that have the capacity to generate radioisotopes. To use the analogy of the mousetrap, pretend you have a mousetrap that catches 100 mice per year. Someone invents a trap that’s expensive to produce so the cost to the consumer is twice as high, but it’s only been shown to catch 102 mice per year. Would you run right out and buy it? Probably not.

The search for better imaging continues, but in the meantime, mpMRI continues to be a PCa dream come true.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.