Prostate cancer: Can imaging substitute for repeat 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 have the cancer monitored and treated only if it shows signs of progression. This is called active surveillance.

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

A newer type of imaging provides an alternative. Called multiparametric magnetic resonance imaging (mpMRI), it allows doctors to visualize prostate cancer from outside of the body. This type of scanning has become more widely adopted for active surveillance, and “may help to reduce the frequency of subsequent repeat biopsy, particularly among men with stable PSA,” says Dr. Boris Gershman, a urologic surgeon at Beth Israel Deaconess Medical Center in Boston, and a member of the Harvard Medical School Annual Report on Prostate Diseases advisory board.

Studying mpMRI’s effectiveness

One outstanding question is if mpMRI can substitute for a “confirmatory biopsy” that men typically get a year or so into the monitoring process to see if the cancer is still stable. The risk is that an mpMRI could miss worsening cancer that a confirmatory biopsy would otherwise detect.

To investigate, a team of Australian researchers performed a newly published study. They enrolled 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 on an active surveillance protocol for three years. They got PSA checks every six months, yearly digital rectal exams, and an mpMRI scan at the end of years one and two. If the PSA and/or mpMRI findings suggested worsening cancer, then the men had a biopsy. If not, biopsies were delayed until the study wrapped up three years later.

Upon analyzing the results, the team found that mpMRI scans were better at ruling out cancer progression than at detecting it. Specifically, the odds that an mpMRI scan would detect clinically significant cancer (the kind that needs more immediate treatment) that a biopsy would later confirm ranged from 50% to 57%. By contrast, the odds that a scan would correctly show the absence of worsening cancer ranged between 82% and 86%.

Conclusions and caveats

Based on these results, the investigators concluded that men with negative mpMRI scans can safely omit the one-year confirmatory biopsy. However, men should still get a standard three-year biopsy, they wrote, “due to occasional MRI-invisible tumors.” The team plans to follow the men and present 10-year data at some point in the future.

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

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