MRI Combination Techniques Hone Accuracy of Prostate Cancer Diagnosis

Published: Monday, Jul 02, 2018
Andre Luis de Castro Abreu, MD

Andre Luis de Castro Abreu, MD

Several studies presented at this year’s American Urological Association (AUA) meeting underscored the value of multiparametric magnetic resonance imaging (mpMRI) in the diagnosis and management of prostate cancer. According to the findings, the use of mpMRI in combination with other tools for diagnosis can reduce unnecessary prostate biopsies. They also indicated that use of mpMRI is on the rise, particularly in men aged 60 to 65.

A retrospective study of 401 patients with negative findings from mpMRI testing (PI-RADS score <3 or Likert score <3) sought to determine whether mpMRI could identify patients most likely to benefit from biopsy.1

A negative mpMRI with no prior biopsies and a low prostate-specific antigen (PSA) density (PSAD) enabled investigators to rule out the presence of clinically significant (Gleason score ≥ 3+4) and high-grade (Gleason score ≥ 4+3) prostate cancer with a high degree of accuracy.

The combination of a negative mpMRI, negative biopsy history, and PSAD <0.15 ng/mL/cc was associated with a negative predictive value (NPV) of 95%. With a higher PSAD and a non-negative prostate biopsy history, NPV declined by more than 20%. The results led investigators to propose an MRI-based algorithm for determining the need for prostate biopsy.

“If the MRI suggests a clinically suspicious lesion, we perform a biopsy; if the MRI is negative, we look at the patient’s biopsy history,” said Andre Luis de Castro Abreu, MD, at the meeting, held May 18 to 21 in San Francisco, California. “If the patient never had prostate biopsy, it is probably better to perform a biopsy.

“If the patient had a prior negative biopsy, we then assess the markers, and if the levels are high or suspicious, the patient has a biopsy. If not, then the patient may avoid a prostate biopsy,” said Abreu, an assistant professor of clinical urology at the University of Southern California, Los Angeles.

The study population included 107 patients with no prior biopsy, 212 with prior negative biopsy, and 79 with prior positive biopsy. Biopsy results revealed cancer in 34% of the patients, including clinically significant prostate cancer in 11% and high-grade cancer in 5%. MRI alone had an NPV of 95% for highgrade prostate cancer, 89% for clinically significant cancer, and 66% for any prostate cancer.

The biomarker analysis showed that PSAD had significant discriminatory power for distinguishing clinically significant from insignificant cancer (P <.01) and from benign disease (P <.001). For a subgroup of patients with a prior negative biopsy (n = 128), pairing a negative mpMRI and PSAD cutoff of <0.15 ng/mL/cc produced an NPV of 95%. Further lowering of the PSAD cutoff further improved NPV but with a trade-off of excluding substantially more patients.

The study is the largest to date to evaluate the combination of a negative MRI and PSAD for ruling out clinically significant and high-grade disease. The results are in line with those of the previous research, which yielded NPV values of 89% to 100%, Abreu said.

A recent review showed that previous studies of MRI to detect clinically significant prostate cancer yielded NPVs of 63% to 96%, as determined by biopsy or prostatectomy specimen.2 Results of a large, multicenter study published last year suggested that triage by mpMRI could eliminate 25% of unnecessary prostate biopsies.3 However, NPV ranged between 72% and 89%, depending on the definition of clinically significant prostate cancer.

Figure. PSA Test Compliance Rate Significantly Higher than Biopsy Compliance Rate6

Combining PHI and mpMRI

The Prostate Health Index (PHI) and mpMRI have been used independently to predict prostate cancer grade reclassification (Gleason score >6) for patients on active surveillance (AS). Results from a study reported at the AUA meeting showed that combining these tools would have enabled more accurate prediction of grade reclassification at surveillance biopsy than use of mpMRI or PHI alone. Further, the combination of these tools would have eliminated the need for repeat biopsy in about 20% of cases.4

Biopsy requirements associated with AS are a major contributor to noncompliance (Figure),5,6 and identifying methods that would safely reduce biopsy burden without missing opportunities to treat cancers that develop high-risk features could improve compliance with AS, said lead author Zeyad R. Schwen, MD, a urology resident at Johns Hopkins University in Baltimore, Maryland.

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