The use of multi-parametric magnetic resonance imaging (mpMRI) could help avoid a repeat prostate biopsy in some men, according to a new study. The imaging test has a high sensitivity for clinically significant cancers, but could miss some and overdiagnose insignificant cancers as well.
“The prostate cancer diagnostic pathway is very different to that of almost all other solid organ cancers, in that it is calibrated to detect subclinical disease but often misses clinically important disease,” wrote study authors led by Lucy A. M. Simmons, MBBS, MRCS, of University College London. That imprecision arises from the use of transrectal ultrasound-guided (TRUS) biopsy, which is considered standard in men with elevated prostate-specific antigen (PSA) levels.
Men often require a repeat biopsy, and the PICTURE trial aimed to compare mpMRI to biopsy in those who do. It included a total of 249 men who underwent both mpMRI and a transperineal prostate mapping (TTPM) biopsy; the mean age was 62 years, the median PSA level was 6.8 ng/ml, and the median number of previous biopsies was 1. The results of the study were published online ahead of print in the British Journal of Cancer.
A total of 209 men had cancer based on the biopsy (84%); 41% had clinically significant disease. On mpMRI, when a Likert score cutoff of 3 was used, 214 men (86%) had a positive test result. The sensitivity was found to be 97.1%, and the specificity was 21.9%; negative predictive value was 91.4%, and positive predictive value was 46.7%. The overall accuracy as assessed by the area under receiver-operating characteristic was 0.74.
This result changes substantially when the researchers used 4 or higher as a positive score. Using that cutoff, the sensitivity was 80.6%, the specificity was 68.5%, the negative predictive value was 83.3% and the positive predictive value was 64.3%.
With the Likert score cutoff of 3, using mpMRI could allow 14% of men to avoid a second biopsy; 41% of clinically insignificant cancers would be detected, and 9% of significant disease would be missed. With the score cutoff of 4, 48% could avoid a biopsy, and 31% of insignificant cancers would be detected while 17% of significant disease would be missed.
The authors concluded that mpMRI could accurately rule out significant prostate cancer in some men; a score of 1 or 2 on mpMRI would mean the probability of significant disease is about 1 in 10. “A man who is currently advised to undergo a repeat biopsy is faced with the alternatives of an inaccurate test, which confers a risk of sepsis (TRUS biopsy) compared with a highly accurate test that requires a general anesthetic and confers other forms of morbidity but lower risk of sepsis (TTPM biopsies),” they wrote. “He and his physician, upon looking at the performance characteristic of mpMRI in an expert center, may wish to use this before a decision about repeating the biopsy.”