Prostate cancer: can imaging replace repeated biopsies during active surveillance?

A new study says yes, but not without limited risks.

If you’ve been diagnosed with low- or intermediate-risk prostate cancer, the good news is that you don’t have to treat it right away. Since the cancer will likely grow slowly (if at all), you can only have the cancer monitored and treated if it shows signs of progression. This is called active surveillance.

More and more men are choosing active surveillance, which involves repeated prostate-specific antigen (PSA) testing and prostate biopsies to check for tumor growth. That way, you can delay — and maybe even avoid — cancer treatment and its side effects. But repeated biopsies can also be painful and stressful, and they come with a low risk of infection.

A new type of imagery offers an alternative. Called multiparameter magnetic resonance imaging (mpMRI), it allows doctors to view prostate cancer from outside the body. This type of scan has become more widely adopted for active surveillance and “may help reduce the frequency of subsequent repeat biopsies, especially in men with stable PSA,” says Dr. Boris Gershman, urological surgeon at Beth Israel Deaconess Medical. Center in Boston, and a member of HarvardMedical School Annual Report on Prostate Diseases Advisory Board.

Studying the effectiveness of mpMRI

One outstanding question is whether mpMRI can replace a “confirmation biopsy” that men typically get about a year into the monitoring process to see if the cancer is still stable. The risk is that an mp-MRI may miss a worsening of the cancer that a confirmatory biopsy would otherwise detect.

To investigate, a team of Australian researchers carried out a recently published study. They recruited 172 men with low- or intermediate-risk prostate cancer and gave them an mpMRI followed by a prostate biopsy. After that, the men were followed under an active surveillance protocol for three years. They underwent PSA checks every six months, annual digital rectal exams, and mpMRI at the end of years one and two. If the PSA and/or pMRI results suggested worsening of the cancer, the men then had a biopsy. Otherwise, biopsies were delayed until the end of the study three years later.

After analyzing the results, the team found that mpMRIs were more effective at ruling out cancer progression than detecting it. Specifically, the odds of an mpMRI detecting a clinically significant cancer (the type that requires more immediate treatment) that a biopsy would confirm later ranged from 50% to 57%. On the other hand, the chances that a scan correctly shows the absence worsening of the cancer varied between 82% and 86%.

Conclusions and caveats

Based on these results, the investigators concluded that men with negative mp-MRIs can safely omit the one-year confirmatory biopsy. However, men should still undergo a standard three-year biopsy, they wrote, “due to occasional tumors not visible on MRI.” The team plans to track the men and present 10-year data at some point in the future.

Other experts are more cautious. Dr. Gershman, for example, expressed concern about the limited ability of mpMRI to detect clinically significant cancer during active surveillance. But he added that despite its limitations, scanning technology is still a useful tool “that should allow for increased time between repeat biopsies in men at low risk of progression.”

“This study provides insight into the utility of mpMRI in the ongoing evaluation of men under active surveillance,” says Dr. Marc B. Garnick, Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center. “The benefit of the study is that more biopsies can potentially be avoided. The downside is that patients understand that MRI is not an equal substitute for biopsy: a negative MRI result can have missed clinically significant cancer.In my own practice, I have used MRI to monitor men, along with digital rectal exams and PSA assessments on active surveillance instead of repeat biopsies, but only with the full understanding of the patient that a small number of potential clinically significant cancers may be missed by this practice.


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