MRI Improves the “Misclassification” of Men with Prostate Cancer Undergoing Active Surveillance

While prostate cancer remains one of 

Active surveillance for prostate cancer: What is it and is it right for me? PART ONE ALL CANCERS ARE NOT CREATED EQUAL PART TWO WHAT DOES IT ENTAIL

the most common cancers  in men in the US, many patients are diagnosed with indolent (or benign-behaving) prostate cancer – cancers that will not affect a man's longevity and do not require treatment. This blog has previously covered the basics of active surveillance (see inset). Over a ten year period of active surveillance, approximately one third of men will undergo a treatment for their prostate cancer. The majority of those men, approximately 70%, elected treatment due to an increased volume of cancer or Gleason score > 6 – indicating the presence of more aggressive cancer.[1] Determining who has high-grade or aggressive prostate cancer at the outset can be challenging based on traditional biopsy techniques. Dr. H. Ballentine Carter, MD, Professor of Urology and Director of the Active Surveillance Program at the Brady Urological Institute explains,

"Misclassification is the problem of relying on a prostate biopsy, which samples only a small fraction of the prostate, to reflect the biology of the entire gland. If a diagnosis of low-grade prostate cancer is made on the prostate biopsy and the patient chooses active surveillance, the risk that a higher-grade, more aggressive cancer is present within the prostate can range from 10 to 30 percent."

MRI (Magnetic resonance imaging) makes use of high-powered magnets and their influence on molecules like water (H2O) to image the body. Multi-parametric MRI (mpMRI) uses complex computer algorithms to differentiate benign from malignant tissue and has demonstrated promise in better identifying patients suitable for active surveillance. This technology relies on three characteristics of prostate cancer cells:

1. Prostate cancer cells are abnormal and can emit MRI signals different than normal tissue
2. Because cancer cells are disorganized relative to normal prostate tissue, surrounding water diffuses through cancerous tissue differently than through normal prostate
3. Cancers form with new blood vessels, these new blood vessels create abnormal diffusion of contrast materials through cancer and normal tissue

In addition, some prostate cancers can hide in areas of the prostate difficult to reach with a standard, transrectal ultrasound-guided biopsy. By assessing all of these characteristics and viewing these "hard to reach places," mpMRI can detect prostate cancers missed on biopsy.

In a recent study of 96 men on active surveillance at Johns Hopkins, Carter, with radiology colleagues Sayed Dianat and Kasia Macura, found that men with a mpMRI abnormality had a cancer 41% of the time, compared to 8% of men with a normal mpMRI. This resulted in a 65% lower risk of adverse pathology on subsequent biopsy if an active surveillance patient had a normal mpMRI.[2] 
"Our group demonstrated that when mpMRI suggested the absence of prostate cancer in a particular area of the prostate, there was a high probability that cancer was absent on multiple biopsies taken from these negative mpMRI areas."

"We are now using mpMRI routinely to help select the most appropriate candidates for active surveillance, and to help reduce the frequency of biopsies."

Therefore, mpMRI can help identify men who truly have low-risk prostate cancer, reducing the "misclassification" of these men and decreasing the number of biopsies needed in the future.

Portions of this story were extracted from "Making Active Surveillance Safer" in Discovery: Volume XI, Winter 2015 by the Patrick C. Walsh Prostate Cancer Research Fund.

 
[1] Tosoian JJ, Trock BJ, Landis P, Feng Z, Epstein JI, Partin AW, Walsh PC, Carter HB. Active surveillance program for prostate cancer: an update of the Johns Hopkins experience. J Clin Oncol. 2011 Jun 1;29(16):2185-90. doi: 10.1200/JCO.2010.32.8112. Epub 2011 Apr 4. http://jco.ascopubs.org/content/29/16/2185.long
[2] Dianat SS, Carter HB, Pienta KJ, Schaeffer EM, Landis PK, Epstein JI, Trock BJ, Macura KJ. Magnetic Resonance-invisible Versus Magnetic Resonance-visible Prostate Cancer in Active Surveillance: A Preliminary Report on Disease Outcomes. Urology. 2015 Jan;85(1):147-54. doi: 10.1016/j.urology.2014.06.085. Epub 2014 Oct 16. http://www.goldjournal.net/article/S0090-4295(14)00915-7/abstract