Did you ever notice how common phrases in English tend to morph over time into funny alterations? For example:

• It’s a dog-eat-dog world becomes “It’s a doggy dog world”
• For all intents and purposes evolves into “For all intensive purposes”
• White as a sheet turns into “White as a sheep.”

Here’s my favorite: The proof of the pudding is in the eating, which has shortened into “The proof is in the pudding.” I’m not sure how pudding would be proof of anything, but at least the shortened version still conveys the meaning, “It just goes to show you.”

Sometimes patients who come in for a prostate MRI ask me, “How can you prove that what the MRI shows is really prostate cancer?” Coming from a worried patient, that’s an understandable question. Cancer is a serious matter. As such, it needs to be accurately diagnosed to ensure a treatment plan with the highest potential for success. And accurate detection is the key step toward diagnostic proof.

Detection vs. diagnosis

There is a difference between PCa detection and PCa diagnosis. Think of it like this: You’re peacefully asleep when a sudden loud noise wakes you up. Your ears picked up something unexpected that rouses you. That’s detection. But what made the noise? A storm rolling in? An intruder breaking glass? One is less threatening than the other, so it’s important to identify the source as accurately and quickly as possible. Aha! A flash of lightning followed by a second clap of thunder tells you what you need to know. That’s diagnosis. Appropriate action is called for if you left windows open and you don’t want to face damp carpets in the morning.

With PCa, there are two levels of “proof.” Level one is detection, which is done by a PSA blood test followed by imaging. These two tests together “prove” whether or not a biopsy is needed. If so, level two is diagnosis, which is done by means of a needle biopsy. In other words, if the imaging picks up one or more areas that look like significant prostate cancer, that’s detection. And, if the biopsy is positive, it’s proof that PCa is present. Appropriate action is called for, determined in discussion with your doctor.

Multiparametric MRI identifies significant prostate cancer

“Okay,” you say, “but how reliable is MRI detection? I don’t want to have a biopsy if I really don’t need one.” That’s understandable. Conventional methods of PCa detection (PSA blood test) and diagnosis (random TRUS biopsy) gained a sad track record of false alarms. After all, the PSA blood test is not specific only for PCa, and TRUS biopsy found many low-risk tumors that might never have become life-threatening but were immediately sent for aggressive treatment that left too many men with sexual, urinary, and bowel side effects.

Thankfully, today’s multiparametric MRI (mpMRI) has demonstrated high accuracy in not only picking up suspicious tumors, but also rating the probability that they are significant (likely to become dangerous). In fact, a newly published paper summarizes MRI’s performance in separating “the sheep from the goats,” that is, the indolent slow-growing lesions (unlikely to become life-threatening) from the aggressive areas. The authors reviewed 16 studies involving over 4,900 patients and statistically analyzed their results in terms of how well MRI correctly predicted the presence and absence of significant PCa.^[i]

The studies spanned 11 years (2013-2024), so the average results included early years when imaging was less well developed than it is now, and of course the more recent years when accuracy is improved. They found that on average, mpMRI was 88% accurate for detection of significant PCa. Other reviews that include only more recent articles have found accuracy rates as high as 96-98%.^[ii]

Again, these are detection rates, not diagnostic rates—but the point is, MRI gets high marks for accurately determining who needs a biopsy and who doesn’t. To paraphrase the adage about pudding, the proof of the next step is in the imaging.

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

References

[i] Yang L, Zhang T, Liu S, et al. Diagnostic Performance of Multiparametric MRI for the Detection of suspected Prostate Cancer in Biopsy-Naive Patients: A Systematic Review and Meta-analysis. Acad Radiol. 2024 Sep 2:S1076-6332(24)00590-7.
[ii] Ahmed, Hashim U et al. Diagnostic accuracy of multi-parametric MRI and TRUS biopsy in prostate cancer (PROMIS): a paired validating confirmatory study. The Lancet, Volume 389, Issue 10071, 815 – 822.