In a study of population-based screening by invitation, the results showed that among men with elevated PSA levels, combined biopsy performed only in men who had positive results on magnetic resonance imaging (MRI) was non-inferior to standard biopsy for detecting clinically significant prostate cancer. The markedly reduced incidences of unnecessary biopsy and diagnosis of clinically insignificant cancer address key barriers impeding implementation of population-based screening for prostate cancer.
The reduced biopsy rate and potential downstream savings that result from less overtreatment offer potential cost savings that may offset the additional costs of MRI according to STHLM3-MRI researchers, who presented the findings at the 36th Annual Congress of the European Association of Urology (8-12 July 2021) and published simultaneously in The New England Journal of Medicine.
The authors wrote in the study background that prostate cancer screening in which PSA testing is followed by standard ultrasound-guided, transrectal prostate biopsy in men with elevated PSA levels reduces prostate cancer mortality. However, PSA-based screening also leads to high rates of overdiagnosis and overtreatment of clinically insignificant prostate cancer and to many unnecessary biopsies. MRI-directed biopsy has shown the potential to address this challenge, but the implications of its use in the context of organised prostate cancer screening are unknown.
The STHLM3-MRI study compared several different screening strategies that used combinations of risk prediction, MRI-directed biopsy, and standard biopsy in a population-based, organised screening by invitation design.
The study team invited men between 50 and 74 years of age from the general population to participate; those with PSA levels of 3 ng per milliliter or higher were randomly assigned in a 2:3 ratio to undergo a standard biopsy or MRI-directed and standard biopsy if the MRI results suggested prostate cancer. The primary outcome was the proportion of men in the intention-to-treat (ITT) population in whom clinically significant cancer with a Gleason score ≥7 was diagnosed. A key secondary outcome was the detection of clinically insignificant cancers in case of Gleason score 6.
Among 12,750 enrolled men, 1532 had elevated PSA and were randomly assigned to undergo biopsy. In particular, 603 were assigned to the standard biopsy and 929 to combined MRI-directed and standard biopsy.
In the ITT analysis, clinically significant cancer was diagnosed in 192 men (21%) in the combined biopsy group, as compared with 106 men (18%) in the standard biopsy group (difference 3 percentage points; 95% confidence interval [CI] −1 to 7; p < 0.001 for non-inferiority).
The percentage of clinically insignificant cancers was lower in the combined biopsy group than in the standard biopsy group, 41 men (4%) versus 73 men (12%) with difference of −8 percentage points (95% CI −11 to −5).
The authors commented when normalised to a population of 10,000 men between 50 and 74 years of age, in which those with elevated PSA levels are referred for biopsy, the combined biopsy approach in men with positive MRI scans would result in 409 fewer men undergoing biopsy, 366 fewer biopsies with benign findings, and 88 fewer clinically insignificant cancers detected than with the standard biopsy approach. These numbers represent 48%, 73%, and 62% lower incidences, respectively, with the use of MRI and the combined biopsy approach.
In conclusion, population-based screening showed that men over age 50 with elevated PSA and negative MRI results could safely forgo biopsy. Detection of clinically significant cancer among men with positive MRI results who underwent MRI-directed and standard biopsies was similar to that in the standard biopsy group, but the MRI group had fewer findings of clinically insignificant cancers.
The study was supported by the Swedish Research Council, the Swedish Cancer Society, the Percy Falk Foundation, the Magnus Bergvall Foundation, the Strategic Research Program on Cancer (StratCan) at Karolinska Institutet, the Hagstrand Memorial Fund, Region Stockholm, Svenska Druidorden, Åke Wibergs Stiftelse, and Swedish e-Science Research Center, Karolinska Institutet, and the Swedish Prostate Cancer Foundation.
Eklund M, Jäderling F, Discacciati A, et al. MRI-Targeted or Standard Biopsy in Prostate Cancer Screening. NEJM; Published online 9 July 2021. DOI: 10.1056/NEJMoa2100852