MRI Is 'Feasible' Prostate Cancer Screening Test

Nick Mulcahy

July 19, 2016

Last year, the Sunnybrook Health Sciences Centre ran a 1-week ad in the print edition of the biggest local newspaper, the Toronto Star, seeking volunteers for the first study of MRI as a prostate cancer screening tool.

The response was "overwhelming," said lead study author Robert Nam, MD, a urologist at the center, which is affiliated with the University of Toronto in Ontario, Canada.

"It's amazing. We had 300 responses [for 50 study slots]," he told Medscape Medical News.

Dr Nam and his fellow researchers expected a lesser reaction.

After all, the study design was a bit off-putting — participants had to undergo a mandatory prostate biopsy, regardless of their screening results. Also, there was no financial compensation.

But some laymen appear to believe in MRI for screening or at least want to give it a try. "Men enthusiastically want it," said Dr Nam.

The study results, which are published online in the August edition of the Journal of Urology, indicate that MRI is a "feasible" primary screening test for prostate cancer for the general population.

"Patients are willing to undergo MR and patients are willing to rely on the MR to guide treatment," said Dr Nam, summarizing the two main feasibility findings.

 
Patients are willing to undergo MR. Dr Robert Nam
 

Of the 50 enrolled patients, 47 had full results; 18 (38.3%) had cancer and 29 (61.7%) had no evidence of cancer. The patients were age 50 to 75 years (median, 61 years), were from the general population, and had no known family history. Each man underwent a digital rectal examination, prostate-specific antigen (PSA) test, 3-T multiparametric MRI, and then, finally, biopsy.

Notably, MRI was nearly 3 times better than PSA at diagnosing prostate cancer.

Specifically, the adjusted odds ratio (OR) of prostate cancer was significantly higher for MRI score than for PSA level (2.7 [95% confidence interval (CI), 1.4 - 5.4; P = .004] vs 1.1 [95% CI, 0.9 - 1.4; P = .21]).

MRI also performed much better than PSA in predicting aggressive prostate cancer (Gleason score of 7 or more).

The adjusted OR of aggressive cancer was again significantly higher for MRI score than for PSA (3.5 [95% CI, 1.5 - 8.3; P = .003] vs 1.0 [95% CI, 0.9 - 1.2; P = .58]).

The pilot study results were satisfactory enough that the Sunnybrook team has started the first randomized clinical trial of MRI vs PSA for prostate cancer screening in the general population. Enrollment is brisk in the single-center trial, said Dr Nam: "We are getting the same kind of dramatic response."

A prostate cancer expert not involved with the study focused her enthusiasm for MRI on its use in cancer diagnosis, not screening.

"In the world of prostate cancer detection, prostate MRI is one of the most exciting new developments. For example, we can finally target specific imaging-detected lesions on prostate biopsy, as is done in other solid organs, greatly increasing sampling efficiency," said Stacy Loeb, MD, a urologist at New York University in New York City.

"We do not yet have enough information to recommend that MRI should be used as an initial screening test," she said in an email to Medscape Medical News.

Furthermore, in a brief editorial that accompanies the study, a pair of urologists highlight several shortcomings.

"The sensitivity of multiparametric MRI for cancer detection is not reported and a clear threshold for biopsy could not be ascertained," write Xiaosong Meng, MD, PhD, and Samir S. Taneja, MD, both of whom are also from New York University. The pair are also concerned that the imaging could actually increase — not decrease — unnecessary biopsies.

Study Details and More About Biopsies

In the pilot study, one uroradiologist with extensive MRI experience reviewed the scans to identify all lesions. The study authors admit that "interobserver variability" in interpreting MRI scans is a potential weakness with any would-be widespread use of MRI as a prostate cancer screening tool.

They also write that "automated techniques to extract prognostic information from MRI may help address the variability inherent in MRI interpretation."

Nevertheless, in the study, the presence or absence of cancer on MRI was scored on a 5-point scale according to recent European Consensus Guidelines, with scores dichotomized as 3 or less and 4 or greater.

As part of their analysis, the researchers divided patients into normal PSA (less than 4.0 ng/mL) and abnormal PSA (4.0 ng/mL or greater) groups and compared their respective MRI score along with their biopsy results.

Prostate cancer was ultimately diagnosed in 9 of the 30 men (30.0%) with normal PSA.

Among these 30 men, the positive predictive value (PPV) in patients with an MRI score of 4 or more was 66.7% (6 of 9) and the negative predictive value (NPV) in patients with an MRI score of 3 or less was 85.7% (18 of 21; chi-square test P = .004).

Both of these results are better than that with PSA testing, say the authors. "For patients with normal PSA (less than 4.0 ng/ml) MRI significantly improved PPV and NPV for prostate cancer," they write.

MRI might address two big weaknesses of the PSA test, said Dr Nam.

First, "PSA underdetects aggressive cancers that actually do need treatment," he said. In the new study's discussion section, he and his coauthors cite the Prostate Cancer Prevention Trial and observe that, in the placebo group, the prevalence of high-grade cancer was 12.5% among men with PSA less than 0.5 ng/mL and up to 25% among those with PSA of 3.1 to 4.0 ng/mL. In short, the negative predictive value needs improving.

Second, "PSA lead to overdiagnosis of nonaggressive prostate cancer," Dr Nam said, adding that unnecessary biopsy and treatment follow. MRI could improve upon the PPV here, he said.

Citing other research, the study authors say that MRI could reduce unnecessary biopsies "in almost a quarter of patients with suspicion of prostate cancer due to elevated PSA or abnormal DRE" (J Urol. 2016;195:1428-1435).

 
[T]his type of screening carries the risk of escalating and not reducing the number of biopsies. Dr Xiaosong Meng and Dr Samir S. Taneja
 

But the editorialists see some of these issues very differently.

They observe that many men in the study with a normal PSA result had an MRI abnormality, and they believe that interpreting MR images is "highly variable." Given the possible combination of these factors in the real world, Dr Meng and Dr Taneja worry that "implementing this type of screening carries the risk of escalating and not reducing the number of biopsies and, secondarily, over detection."

In discussing the new study results, Dr Nam focused on the feasibility findings. "Don't focus on the numbers," he said about the other data. The small sample size is a study limitation and does not allow for "definitive conclusions" regarding the accuracy of MRI in prostate cancer screening.

 
Don't focus on the numbers Dr Robert Nam
 

Finally, the study authors acknowledge that MRI is more costly and less portable than a PSA test.

"The obvious downside of using prostate MRI for prostate cancer screening in the general population would be the high cost and availability of MRI," they write.

But MRI has the potential to reduce downstream costs, they observe.

"The potential savings resulting from detecting and treating aggressive prostate cancer at an earlier stage, and avoiding unnecessary prostate biopsy and treatment of indolent prostate cancer could justify the cost of prostate MRI screening," they write.

The authors have disclosed no relevant financial relationships. Dr Loeb is an advisor to Bayer.

J Urol. 2016;196:361-366. Abstract Editorial

Follow Medscape senior journalist Nick Mulcahy on Twitter: @MulcahyNick.

Follow Medscape Oncology on Twitter: @MedscapeOnc

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