Few significant prostate cancers are undetected by mpMRI

July 22, 2020

Cancers that are missed by mpMRI are significantly smaller and less aggressive than those that are detected.

Only a small proportion of clinically significant prostate cancers are overlooked by multiparametric magnetic resonance imaging (mpMRI), according to findings from a post hoc analysis of the Prostate MRI Imaging Study (PROMIS).

The cancers that are missed by mpMRI are significantly smaller and less aggressive than those that are detected.

Of men with prostate cancer in PROMIS, 4.4% to 17% had their cancers undetected by mpMRI, depending on the definition of clinical significance used, said Joseph M. Norris, BM, BS, during the 2020 European Association of Urology Virtual Congress.1

“The reassuring findings that we show further reinforce the role that MRI should play in a modern prostate cancer diagnostic pathway,” said Norris, specialist registrar in urologic surgery, University College, London, United Kingdom.

The traditional approach of combining serum prostate-specific antigen (PSA) with systematic transrectal ultrasound (TRUS)-guided biopsy is an imperfect risk stratification approach for patients with suspected prostate cancer. Prebiopsy mpMRI has greatly improved the utility of this strategy; “however, as with all diagnostic strategies for prostate cancer, there is a given spectrum of disease that goes undetected or overlooked,” Norris said. “The PROMIS study gives us a unique opportunity to study the nature of MRI-undetected prostate cancer.”

In PROMIS, 576 biopsy-naïve men with suspected prostate cancer and PSA concentrations up to 15 ng/mL underwent prebiopsy mpMRI followed by a combined biopsy procedure consisting of a systematic TRUS-guided biopsy and a 5-mm transperineal template mapping biopsy. In this post hoc analysis, disease was categorized as either mpMRI-detected (Likert score 3 to 5) or mpMRI-undetected (Likert score 1-2). Disease was stratified into 2 forms of clinical significance: definition 1 was overall Gleason score ≥ 4 + 3 of any length or maximum cancer core length (MCCL) ≥ 6 mm of any grade; definition 2 was overall Gleason score ≥ 3 + 4 of any length or MCCL ≥ 4 mm of any grade. Key cancer outcomes were compared between these 2 groups.

“By taking this approach, we demonstrated that the proportion of prostate cancer that is overlooked by mpMRI is low for both definitions of clinical significance,” he said.

Significant prostate cancer was not detected by mpMRI in 17 of 230 men (7%; 95% CI, 4.4%-12%) according to definition 1 cancer and in 44 of 331 men (13%; 95% CI, 9.8-17%) according to definition 2.

Furthermore, prostate cancer that was not detected by mpMRI was significantly lower in overall Gleason (P = .0007) and maximum Gleason scores (P < .0001) and shorter MCCL (median difference: 3 mm [5 vs 8 mm]; P <.0001) compared with detected disease.

No tumors with an overall Gleason score > 3 + 4 or maximum Gleason score > 4 + 3 on transperineal template biopsy were undetected by mpMRI.

Application of a theoretical PSA density threshold ≥0.15, above which a biopsy would be indicated in men with a negative mpMRI, further reduced the proportions of missed disease for both definitions of clinical significance, Norris said. Using this PSA density threshold, the proportion of men with undetected disease was reduced to 5% for definition 1 cancer and to 9% for definition 2 cancer.

Application of a PSA density threshold ≥0.10 to negative mpMRI lowered the proportion of men with undetected disease to 3% for both definition 1 and definition 2 cancer.

When asked about the value of mpMRI alone versus the addition of PSA density to mpMRI findings, Norris said, “This is certainly something we do in the UK, as advised by [the National Institute for Health and Care Excellence] as of last year. The other evidence that we showed in my study is limited slightly in that it’s based upon a 5-mm template mapping biopsy in conjunction with PSA density, which is not something that is really recreated in a real clinical setting. However, using PSA density with mpMRI is a correct approach.”

Disclosure: Norris reports receiving funding from the Medical Research Council.

Reference

1. Norris JM, Echeverria L, Bott SRJ, et al. Which prostate cancers are overlooked by mpMRI? An analysis from PROMIS 2020 European Association of Urology Virtual Congress. July 17-26, 2020.

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