Prostate cancers that are classified as “low risk” based on conventional prostate biopsy and histology are frequently found to be higher risk when assessed using the newer targeted biopsy method, US researchers have warned.
The findings are important because men believed to have indolent cancers are often managed using active surveillance rather than definitive treatment, potentially allowing aggressive tumours more time to grow and metastasise.
“In men initially diagnosed with low-risk prostate cancer, multiparametric magnetic resonance imaging [mpMRI]-ultrasound confirmatory biopsy, including targeting suspicious lesions seen on MRI, resulted in frequent detection of tumors exceeding the Epstein criteria”, write Leonard Marks and co-authors from the University of California in Los Angeles in the Journal of Urology.
“These data suggest that the Epstein criteria be reevaluated in men enrolling in active surveillance to account for the risk inflation seen with targeted prostate biopsy.”
Marks et al identified 113 men with prostate cancer who were enrolled in an active surveillance programme because they met the 1994 Epstein histological criteria for indolent tumours (Gleason score of 6 or less, 2 or fewer positive cores and ≤50% of all cores), and were thus considered to have very low-risk or low-risk disease.
An average of 10 months after diagnosis, the men underwent targeted biopsy using mpMRI. This technique assigns an “image grade” of 1 to 5 to regions of interest, with higher scores indicating a higher degree of suspicion. Four cores were taken for targeted biopsy and an additional 12 cores were taken for repeat systematic biopsy.
On confirmatory biopsy, 38 men (33.6%) were found to be free of prostate cancer, 35 (31.0%) had prostate cancer that fulfilled the Epstein criteria and 41 (36.3%) were reclassified as having prostate cancer that exceeded the Epstein criteria.
Among the latter group, 26 men (23.0%) were reclassified due to having a Gleason score of 7 or higher, and 15 (13.3%) had a Gleason score of 6 but a higher volume of disease.
The proportion of men who were reclassified after confirmatory biopsy was 27.0% among those with a mpMRI image grade 0 to 3, 46.9% among those with grade 4 and 100% in those with grade 5.
Two baseline factors predicted subsequent reclassification: mpMRI image grade of 4 to 5 as opposed to 2 or 3, and a 0.10 U increase in prostate-specific antigen density, with odds ratios of 3.2 and 2.41, respectively.
Of note, findings from standard and new biopsy techniques were concordant in just 50% of cases. Targeted biopsy detected significant cancer in three (3.0%) men considered cancer-free by systematic biopsy, whereas systematic biopsy detected significant cancer in 10 (11.0%) men in whom targeted biopsy found no cancer.
The authors conclude: “Criteria for active surveillance should be reevaluated when mpMRI–ultrasound fusion guided prostate biopsy is used.”
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