What is MRI’s role in early prostate cancer?

Ottawa-The modern response to an elevated PSA is the use of high-quality, well-reported magnetic resonance imaging (MRI), and depending on the outcome of the imaging, a biopsy may follow, says Mark Emberton, MD, of University College, London. 

Also see: Fusion biopsy increases detection of high-grade PCa

In a State-of-the-Art lecture at the Canadian Urological Association annual meeting in Ottawa, Dr. Emberton said that MRI is here to stay largely because biopsying a prostate when the location of the cancer is known is more efficient in detecting clinically significant disease than random biopsying.

"I do not know any urologist who would not order an MRI prior to a biopsy. There is no downside. It is just a question of time and money. It will allow the opportunity to avoid a biopsy if you believe in the negative predictive value of the scan. If you see an abnormality, it makes sense to direct your needle to the abnormality. In all other cancers, we just do targeted biopsies," said Dr. Emberton in an interview with Urology Times.

Data from a study published earlier this year concluded targeted MR/ultrasound fusion biopsy, compared with standard extended-sextant ultrasound-guided biopsy, was linked to increased identification of high-risk prostate cancer and reduced identification of low-risk prostate cancer (JAMA 2015; 313:390-7).

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Moreover, another study published in late June found no additional value of a combined biopsy approach using targeted MRI-ultrasound fusion-guided biopsy and systematic transrectal ultrasound-guided biopsy (TRUS-GB), compared to targeted MRI-guided in-bore biopsy (Eur Urol, June 23, 2015).

Next: MRI challenging to master

Dr. Emberton conceded that MRI is a challenging technique to master, and obtaining really good images is difficult.

With the publication of Prostate Imaging-Reporting and Data System v2, a joint effort of the American College of Radiology and the European Society of Urogenital Radiology, the interpretation of MRI results in prostate cancer should be raised to a level comparable to where MRI interpretation is in breast cancer, said Dr. Emberton.

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"Radiologists have typically written a narrative about what they have seen, which seems to be an inefficient way of describing spatial relationships and intensities. MRI information has to be depicted in a pictoral and probabilistic manner, and consensus groups have agreed on this. This is what you (urologists) should be demanding from radiologists. The sad fact is that MRI information is not written in that manner. I suspect that there will eventually be dedicated and credentialed uro-radiologists who will report MRIs as we do have mammographic experts," said Dr. Emberton.

Numerical interpretation of imaging will provide more useable information to urologists in terms of predicting the probability of cancer, said Dr. Emberton.

"You have to be pretty confident if you are declaring the probability with a number that will mean something. There are operational responses to the numbers (between one and five). If you assign four or five, you will biopsy. If you assign one or two, it means you will watch the patient,” he said.

Next: MRI will not have any incremental utility if it is not used optimally

MRI will not have any incremental utility if it is not used optimally, said Dr. Emberton, explaining the biopsy needs to be "de-coupled" from the PSA.

Currently, nearly all men undergo a biopsy if they have a high PSA score, and no test, until the MRI, can reliably exclude the need for a biopsy in the presence of an elevated PSA score, said Dr. Emberton.

"If you have an MRI after your PSA, you have the opportunity of having a targeted biopsy rather than a random biopsy. We will biopsy fewer men, will biopsy better and will get better risk stratification, and as a result, more appropriate treatment allocation," said Dr. Emberton.

What's more, the tissue that will be sent for pathology will provide a pathologist with rich information, he said.

"When you do a TRUS biopsy and you do not know where the cancer is, you normally miss it because they are small (cancers)," said Dr. Emberton.

A man deemed at low risk of developing prostate cancer undergoes annual biopsies, a frequency that is likely not required, he said.

"Active surveillance only occurs to mitigate the problem of overtreatment. But the best way to avoid overtreatment is to avoid overdiagnosis. MRI allows you to do that," said Dr. Emberton.

Modifications to clinical practice means getting urologists to change their habits, which can be a challenge, he added.

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