Study Shows Adjunctive Benefit of Pre-Biopsy MRI for Diagnosing Prostate Cancer

Could the addition of pre-biopsy magnetic resonance imaging (MRI) enhance conventional prostate cancer screening?

Results from a new study, recently published in Academic Radiology, suggest the combination of MRI and prostate-specific antigen (PSA) testing could prevent prostate biopsy in more than 88 percent of patients without prostate cancer.

In the study of 881 patients who had a pre-biopsy MRI and PSA testing due to suspicion for prostate cancer, 220 patients were diagnosed with prostate cancer and 162 patients had clinically significant cancer. For clinically significant cancer (CSC), the researchers found the combination of pre-biopsy MRI and PSA testing had a significantly higher positive predictive value (PPV) (0.567) than a PSA level greater than or equal to 4 ng/mL alone (0.0219).

While the study authors noted a greater than 25 percent decrease in the sensitivity rate for the tandem of MRI and PSA (0.679 in comparison to 0.938 for PSA alone), they also found the combination had more than triple the specificity rate for CSC (0.833) in comparison to sole reliance on a PSA level greater than or equal to 4 ng/mL (0.248).

“The results meant that more than 88% of patients without prostate cancer could avoid prostate biopsy using the PSA and MRI strategy,” wrote lead study author Moon Hyung Choi, M.D., Ph.D., who is affiliated with the Department of Radiology at the College of Medicine at the Catholic University of Korea, and colleagues. “ROC (receiver operating characteristic) curves of the PSA alone and the (PSA and MRI combination) also showed the difference between the two.”

However, Choi and colleagues did caution against relying solely on MRI results when determining whether a prostate biopsy is necessary. When they employed cutoff values of PI-RADS greater than or equal to 3 and a PSA level greater than or equal to 3 ng/mL, the study authors found that MRI missed 36 percent of all cancers and 30 percent of CSCs.

“Therefore, care should be taken to determine whether to perform biopsy based solely on MRI results,” added Choi and colleagues. “Even in patients with negative MRI, it is necessary to consider additional clinical information to decide on prostate biopsy and to follow-up carefully.”

Yet the researchers did find that as the PSA cutoff level increased, there were corresponding increases in PPVs and decreases in negative predictive values (NPVs) for PSA and MRI.

“For example, even when we considered patients with PSA > 10 ng/mL as positive, only 44% of the patients had prostate cancer, which meant that the PPV of PSA was 0.44. In those patients, the PPV of MRI was much higher (0.86) as MRI could classify the patients according to the likelihood of prostate cancer,” pointed out Choi and colleagues.

In regard to study limitations, the authors noted the emphasis on per patient analyses as opposed to per lesion analyses. Acknowledging the shortcomings of the retrospective study design, the researchers cited a lack of consistency with radiology reports due to the varied experience of those assessing the prostate MRI scans, and a lack of access to PI-RADS reports for some of the study patients. Despite 3T MRI having advantages over 1.5T MRI, Choi and colleagues pointed out that 1.5T MRI scanners were utilized for nearly 70 percent of the MRI exams in the study.