Prostate lesions invisible by MRI: are they dangerous?

Prostate lesions invisible by magnetic resonance imaging. It sounds like science fiction and fantasy stuff, a brainchild of HG Wells, who wrote The invisible manor JK Rowling, author of the harry potter series.

But prostate lesions invisible by MRI are real. And what these injuries may or may not indicate is the subject of intense debate.

MRI plays a role increasingly important role in the detection and diagnosis of prostate cancer, the staging of prostate cancer and the monitoring of disease progression. However, sometimes a puzzling phenomenon arises. Certain prostate lesions that appear when pathologists examine biopsied tissue samples under a microscope are not visible on MRI. Instead, the prostate tissue will appear normal to the radiologist’s eyes.

Why are certain lesions invisible with MRI? And is it dangerous for patients if these lesions are not detected?

Some experts believe that these lesions invisible on MRI scans are not a cause for concern.

If the doctor can’t see the cancer on the MRI, then it’s simply not a threat, according to Mark Emberton, MD, a pioneer in prostate MRI 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 do not require routine biopsies.”

Emberton and Klotz compared lesions invisible on MRI with group 1 prostate cancer (Gleason score ≤ 6), the least aggressive category that indicates the cancer is not likely to spread or kill. For patients under active surveillance, those with cancers invisible to MRIs have dramatically better outcomes than those with visible cancers, Klotz explained.

But other experts in the field are skeptical that MRI-invisible lesions are truly harmless.

Although statistically an MRI-visible prostate lesion indicates a more aggressive tumor, that is not always the case for all individuals, said Brian Helfand, MD, PhD, chief of urology at NorthShore University Health System, Evanston, Illinois. .

MRIs can lead to false negatives in approximately 10%-20% of patients who have clinically significant prostate cancer, although estimates vary.

In an analysis16% of men without suspicious lesions on MRI had clinically significant prostate cancer identified after undergoing a systematic biopsy. Other analysis found that about 35% of MRI-invisible prostate cancers identified by biopsy were clinically significant.

However, other studies have indicated that negative MRI results accurately indicate that patients are at low risk of developing clinically significant cancers. TO recent JAMA Oncology The analysis, for example, found that only seven of 233 men (3%) with negative MRI results at baseline and who completed 3 years of follow-up were diagnosed with clinically significant prostate cancer.

When a patient has a prostate tumor invisible to MRI, there are a couple of reasons why the MRI may not detect it, the urologic oncologist said. Alexander Putnam ColeMD, assistant professor of surgery, Harvard Medical School, Boston. “One is that the cancer is aggressive but very small,” Cole said.

“Another possibility is that the cancer looks a lot like background prostate tissue, which is something you might expect if you think of it more as a low-grade cancer,” he explained.

He radiologist experience level Interpretation of the MRI can also influence the accuracy of the reading.

But Cole agreed that “in general, MRI visibility is associated with molecular and histologic features of progression and aggressiveness, and non-visible cancers are less likely to have aggressive features.”

Genomic profiling of visible and invisible cancers using MRI confirms this.

According to Todd Morgan, MD, chief of urologic oncology at Michigan Medicine, University of Michigan, Ann Arbor, Michigan, gene expression in visible diseases tends to be related to more aggressive prostate tumors, while gene expression in invisible diseases does not.

In an analysisFor example, the researchers found that four genes: PHYHD1, CENPF, ALDH2and GDF15 – associated with worse progression-free survival and metastasis-free survival in prostate cancer also predicted MRI visibility.

“The genes associated with visibility are essentially the same genes associated with aggressive cancers,” Klotz said.

Next steps after a negative MRI result

What do MRI-invisible lesions mean for patient care? If, for example, a patient has elevated PSA levels but a normal MRI, is a targeted or systematic biopsy warranted?

The overall message, according to Klotz, is that “you don’t have to find them.” Klotz noted, however, that patients with a negative MRI result should still be followed with periodic repeat imaging.

Several essays support this approach of using MRI to decide who needs a biopsy and delaying biopsy in men with normal MRIs.

He recent JAMA Oncology The analysis found that among men with negative MRI results, 86% avoided a biopsy for 3 years, and clinically significant prostate cancer was detected in only 4% of men during the study period – four in the initial diagnostic phase and seven in the 3-year diagnostic phase. follow-up phase. However, during the initial diagnostic phase, more than half of the men with positive MRI results were found to have clinically significant prostate cancer.

Other recent study found that patients with negative MRI results were much less likely to improve to higher Gleason scores over time. Among 522 patients who underwent systematic, targeted biopsy within 18 months of their grade 1 group designation, 9.2% with negative MRI results had tumors reclassified as grade 2 group or higher versus 27% with positive MRI results and 2.3% with negative MRI results. had tumors reclassified as grade 3 or higher group versus 7.8% with positive MRI results.

These data suggest that men with grade 1 cancer and negative MRI results “could avoid confirmatory biopsies until a routine surveillance biopsy in 2 to 3 years,” according to study author Christian Pavlovich, MD, professor of oncology. urology at the Johns School of Medicine at Hopkins University, Baltimore.

Cole used the MRI results to classify who undergoes a biopsy. When a biopsy is warranted, “I typically recommend adding systematic sampling of the other side to evaluate for the presence of non-visible cancers,” he noted.

Sampling prostate tissue outside the target area “adds perhaps 1 to 2 minutes to the procedure and does not dramatically increase morbidity or risks,” Cole said. It can also help “confirm that there is cancer in the MRI target and also confirm that there is no cancer in non-visible areas.”

According to Klotz, if imaging demonstrates progression, patients should receive a biopsy; in most cases, just a targeted biopsy. And, Klotz noted, skipping routine prostate biopsies in men with negative MRI results can save thousands of men from these procedures, which carry risks of infections and sepsis.

Beyond Gleason scores for risk prediction, MRI “visibility is a very powerful risk stratifier,” he said.

Howard Wolinsky is a freelancer based in Chicago. He just completed 14 years on active surveillance. At the end of January, he will moderate a program on lesions invisible on MRI, featuring Emberton, and organized by the patient group Active Surveillance Patients International.