MRI and The Magic 8 Ball

When I was growing up, there was a kid on the block who had one of those Magic 8 Ball toys that could tell the future. You probably know what I’m talking about. It was a black ball with a small round window in which an answer to a yes-or-no question would float into view. For example, if you asked the Magic 8 Ball, “Will I be a rock star?” the answer might be along the lines of “Probably” or “Outlook not so good.” I was not the only one who bugged my parents to get one—to no avail—and the boy who owned this remarkable seer found his popularity greatly enhanced.

As it turns out, my wish for a Magic 8 Ball has come true in a way I never imagined. An interesting study from Dr. Mark Emberton’s group at University College London asks: “Can multiparametric magnetic resonance imaging predict upgrading of transrectal ultrasound biopsy results?”[i] The need for their research sprang from the uncertainty in risk stratification that occurs because of inadequate sampling from a standard transrectal ultrasound (TRUS) biopsy. The TRUS biopsy is much like the Magic 8 Ball in that they both deliver random information with no assurance of reliability.

A patient’s chances of getting the most accurate information about his prostate cancer comes from having a radical prostatectomy when the specimen is then available to be examined, slice by slice, under a microscope. But that is after the fact, too late for the option of a less aggressive treatment if the cancer turned out to be small and not aggressive. Wouldn’t it be great to have accurate advance knowledge of the size, shape and location of any tumor(s)? That way, patients who are qualified for a less aggressive treatment, or for active surveillance, would be confident and comfortable choosing an alternative to prostatectomy.

So besides surgical removal, what’s the next best way to (in Dr. Emberton’s words) “interrogate the whole gland”? His institution uses transperineal template-guided prostate mapping (TPM) biopsy as a whole gland reference. In that approach, which is done under anesthesia, biopsy needles are placed through the perineum – the skin between the scrotum and anus – and samples from the gland are taken every 5mm apart. The location of each sample is recorded and used to recreate a 3D map of any tumor sites, and of course the tissue samples are used to diagnose the Gleason score.

In the University College London study, 194 patients had a TRUS biopsy. 137 were diagnosed with low risk cancer if they met any of these four definitions:

  1. Gleason 3+3 in any cancer core length
  2. Maximum cancer core length <50%, any Gleason score
  3. Gleason 3+3 and maximum cancer core length <50%
  4. Gleason 3+3, maximum cancer core length <50%, PSA <10 ng/mL, and <50% positive cores.

Within 18 months of TRUS biopsy (median time 120 days), the men had multiparametric MRI scans that included T2-weighted, diffusion-weighted and dynamic contrast enhanced sequences; their images were scored on a 5-point scale where 1 = cancer is very unlikely, and 5 = cancer is very likely. Finally, they had TPM biopsy after sufficient healing time from the biopsy. A statistical analysis was done to determine the correlation between MRI scores and TPM diagnosis. Based on TPM biopsy, 45% of the men (62/137) were upgraded. The mpMRI scans that were scored low (a score of 1 or 2) had a very high rate of ruling out aggressive cancer according to each of the above definitions:

Definition 1 75% rate of correctly ruling out high grade disease
Definition 2 100% rate of correctly ruling out high grade disease
Definition 3 83% rate of correctly ruling out high grade disease
Definition 4 100% rate of correctly ruling out high grade disease

The authors concluded that an mpMRI tumor scans that were scored 4 or 5 indicated a “high likelihood” of aggressive disease (which correlated with TPM results of higher Gleason grade and/or significant volume of tumor). On the other hand, “…if a lesion is not seen on mp-MRI, the attribution of low-risk grade or cancer burden is much more likely to be correct.” One of the merits of mpMRI after a TRUS biopsy is the ability to help determine if a patient can safely embark on surveillance, or choose a focal treatment, without a repeat biopsy. In addition, it can identify those with a suspiciously high MRI score who should have a targeted biopsy before making a final treatment decision, so high-grade disease is treated aggressively.

Thus, I don’t need a Magic 8 Ball to know whether mpMRI, together with biopsy, will be the future of prostate cancer diagnosis. Studies like this show me that the answer is “Yes, definitely.”

 


[i] Abd-Alazeez MAhmed HUArya M et al. Can multiparametric magnetic resonance imaging predict upgrading of transrectal ultrasound biopsy results at more definitive histology? Urol Oncol. 2014 Aug;32(6):741-7.

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