MRI-invisible prostate lesions. It sounds like the stuff of science fiction and fantasy, a creation from the minds of H.G. Wells, who wrote The Invisible Man, or J.K. Rowling, who authored the Harry Potter series.
But MRI-invisible prostate lesions are real. And what these lesions may, or may not, indicate is the subject of intense debate.
MRI plays an increasingly important role in detecting and diagnosing prostate cancer, staging prostate cancer as well as monitoring disease progression. However, on occasion, a puzzling phenomenon arises. Certain prostate lesions that appear when pathologists examine biopsied tissue samples under a microscope are not visible on MRI. The prostate tissue will, instead, appear normal to a radiologist’s eye.
Why are certain lesions invisible with MRI? And is it dangerous for patients if these lesions are not detected?
Some experts believe these MRI-invisible lesions are nothing to worry about.
If the clinician can’t see the cancer on MRI, then it simply isn’t a threat, according to Mark Emberton, MD, a pioneer in prostate MRIs and director of interventional oncology at University College London, London, England.
Laurence Klotz, MD, of the University of Toronto, Toronto, Ontario, Canada, agreed, noting that “invisible cancers are clinically insignificant and don’t require systematic biopsies.”
Emberton and Klotz compared MRI-invisible lesions to grade group 1 prostate cancer (Gleason score ≤ 6) — the least aggressive category that indicates the cancer that is not likely to spread or kill. For patients on active surveillance, those with MRI-invisible cancers do drastically better than those with visible cancers, Klotz explained.
But other experts in the field are skeptical that MRI-invisible lesions are truly innocuous.
Although statistically an MRI-visible prostate lesion indicates a more aggressive tumor, that is not always the case for every individual, said Brian Helfand, MD, PhD, chief of urology at NorthShore University Health System, Evanston, Illinois.
MRIs can lead to false negatives in about 10%-20% of patients who have clinically significant prostate cancer, though estimates vary.
In one analysis, 16% of men with no suspicious lesions on MRI had clinically significant prostate cancer identified after undergoing a systematic biopsy. Another analysis found that about 35% of MRI-invisible prostate cancers identified via biopsy were clinically significant.
Other studies, however, have indicated that negative MRI results accurately indicate patients at low risk of developing clinically significant cancers. A recent JAMA Oncology analysis, f