Prostate Cancer: Can Imaging Replace 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 need to treat it right away. Because the cancer is likely to grow slowly (if at all), you can monitor and treat the cancer only if it shows signs of progression. This is called active monitoring.

More men are opting for active surveillance, which includes repeated prostate-specific antigen (PSA) tests and prostate biopsies to check for tumor growth. This way, you can delay—and perhaps even avoid—cancer treatment and its side effects. However, repeated biopsies can also be painful and stressful and are associated with a low risk of infection.

A newer type of imaging offers an alternative. So-called multiparametric magnetic resonance imaging (mpMRI) allows doctors to visualize prostate cancer from outside the body. This type of scanning is becoming increasingly common for active surveillance and "may help reduce the frequency of subsequent repeat biopsies, particularly in men with stable PSA," says Dr. Boris Gershman, a urologic surgeon at Beth Israel Deaconess Medical Center in Boston and a member of theHarvardAnnual report of the Medical Faculty on prostate diseasesAdvisory Board.

Investigating the effectiveness of mpMRI

An open question is whether mpMRI can replace a “confirmatory biopsy,” which men typically include in the surveillance process for about a year 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 this, a team of Australian researchers conducted 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. The men were then tracked for three years as part of an active surveillance protocol. They had PSA checks every six months, annual digital rectal exams, and an mpMRI scan at the end of the first and second years. If PSA and/or mpMRI results suggested worsening of the cancer, the men underwent a biopsy. If not, biopsies were postponed until the study was completed three years later.

When they analyzed the results, the team found that mpMRI scans were better at ruling out cancer progression than detecting it. Specifically, the probability that an mpMRI scan would detect clinically significant cancer (the type requiring immediate treatment) that a biopsy would later confirm was between 50% and 57%. On the other hand, the chances that a scan would show this correctly increaseabsenceof worsening cancer was between 82% and 86%.

Conclusions and caveats

Based on these results, the researchers concluded that men with negative mpMRI scans can safely skip the one-year confirmatory biopsy. However, men should continue to receive 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 sometime in the future.

Other experts take a more cautious view. 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, the scanning technology is still a useful tool "that should allow more time between repeat biopsies in men who are otherwise at low risk of progression."

“This study contributes to a better understanding of the utility of mpMRI in the continuous assessment of men on active surveillance,” says Dr. Marc B. Garnick, Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center. "The advantage of the study is that more biopsies may be avoided. The disadvantage is that patients understand that MRI is not an equivalent substitute for biopsy: a negative MRI finding may have missed a clinically significant cancer. I have used MRI for surveillance in men, along with digital rectal exams and PSA evaluations for active surveillance in place of repeat biopsies, but only with the patient's full understanding that a small number of potential clinically significant cancers may be identified by this practice not be recognized.