NPV is a key indicator for future prostate cancer risk

2016 11 21 15 27 14 989 Rsna 2016 400

CHICAGO - Negative predictive values (NPVs) derived from multiparametric MRI scans provide an excellent indication of clinically significant prostate cancer and could help men with a prior negative biopsy avoid unnecessary procedures, according to a study presented on Tuesday at RSNA 2016.

An 11-year review of prostate cancer patients revealed that it may be safe and feasible for these men to receive follow-up by MRI less frequently, even if they have elevated prostate-specific antigen (PSA) levels.

"Our study results show that multiparametric MRI offers an excellent NPV for ruling out clinically significant prostate cancer," said study co-author Dr. Kirsteen Burton, a radiology resident at the University of Toronto. "That is, 96% of men who had a prior negative prostate biopsy and who subsequently received a prostate MRI had a true-negative prostate cancer result over a median follow-up period of just under seven years."

Avoiding biopsy

One way to assess prostate cancer is through biopsy. However, previous research has shown that men often have a decrease in short-term quality of life following the procedure, Burton told AuntMinnie.com. In addition to inconvenience and discomfort, biopsies carry a clinically relevant risk of bleeding or sepsis.

"The more of these we can safely avoid, it is potentially the better for our patients," Burton told RSNA attendees. "Our research question was: What is the negative predictive value of multiparametric MRI with negative biopsies and elevated PSA levels? Our hypothesis was that multiparametric MRI prostate examinations should offer a high negative predictive value for clinically significant prostate cancer and hopefully avoid repeated biopsies in patients."

The researchers retrospectively reviewed all patients who underwent MRI scans at the University of Toronto between 2004 and 2015 for prostate cancer to detect, locate, and/or stage the disease. Patients were excluded from the study if they had a history of ablation, radiation, or prostatectomy; a follow-up of less than two years; a prior biopsy that confirmed prostate cancer; and no available Gleason score. Qualifying subjects' median age was 63 years (range, 38-87 years), and the median follow-up was seven years.

Prior to 2006, the joint medical imaging department used an MRI protocol of T2-weighted and dynamic contrast-enhanced (DCE) sequences. Diffusion-weighted MR imaging (DWI-MRI) was added as third sequence after 2006. A Gleason score greater than 7 indicated the likelihood of prostate cancer.

MRI results

During the 11-year study period, 727 prostate MRI studies were performed, with 541 MRI results included in the analysis. Of those 541 patients, 409 (76%) had an initial positive MRI. Clinically significant cancer was present in 237 of the 409 men at biopsy, for a positive predictive value (PPV) of 58%. Within this group, the PPV of MRI in patients with a prior negative biopsy was significantly lower (17%), compared with patients on active surveillance (63%).

The other 132 men (24%) had a negative initial MRI scan for prostate cancer. Of these patients, 73 had a previous negative biopsy and median PSA of 10, while 59 had low-volume Gleason 6 disease and median PSA of 6. At a median follow-up of 81.4 months, 115 of the men (87%) remained on watchful waiting or active surveillance, with no prostate cancer or clinically significant signs of the disease. In addition, 70 of the 73 men with a previous negative biopsy remained free of clinical disease at the median follow-up, which translated to an NPV of 96%.

Burton cited several strength of the study, including the relatively long follow-up and large sample size. Limitations included the fact that it was a retrospective single-center study.

"The balance of our study overall shows there is promise that multiparametric MRI has high negative predictive value, and for men with negative biopsies and negative MRI, the risk of developing clinically significant prostate cancer at seven years of follow-up is extremely low," Burton said. "Therefore, these could potentially be followed less frequently and potentially receive fewer prostate biopsies in the future."

It may also be safe for men with elevated PSA levels and prior negative prostate biopsies to receive clinical follow-up rather than "unpleasant prostate interventions," she concluded.

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