The most common method, called a systematic biopsy, sometimes misses tumors, and it can also misclassify cancer as being either more or less aggressive than it really is. During systematic biopsy, a doctor takes 12 evenly-spaced samples of the prostate, called cores, while looking at the gland with an ultrasound machine.
Are prostate cancer biopsies reliably accurate?
Not always.
A new method, called MRI-targeted biopsy, guides doctors to suspicious abnormalities in the prostate, and emerging evidence suggests that it’s better at detecting high-grade, aggressive tumors that need immediate treatment. These biopsies require doctors to get an MRI of the prostate first. Computer software then fuses the high-resolution MRI scan with ultrasound images gathered in real time during the biopsy procedure. Since doctors only sample from where the MRI reveals possible evidence of cancer, they can take fewer cores.
Some experts are now saying that systematic biopsies should be replaced by the MRI-targeted approach, even though it requires specialized training, and is generally available today only in large academic cancer centers.
However, new evidence suggests that the best way to reduce diagnostic uncertainties is to take both biopsies together. The findings come from a study performed at the National Cancer Institute in Bethesda, Maryland.
Investigators enrolled 2,103 men with suspected prostate cancer based on abnormal PSA readings and digital rectal exams. Each was given an MRI-targeted biopsy, followed immediately by a systematic biopsy. Cancer was detected in 1,312 of the men, and 404 of them were surgically treated. The investigators wanted to compare the two biopsy methods in terms of being able to find cancer and classify it correctly as high- or low-grade. The surgically removed prostate specimens provided a final confirmation.
As it turned out, 208 more cancers were detected by giving both biopsies together than by giving systematic biopsies alone, and 59 of the additional cancers were in high-risk categories. MRI-targeted biopsies by themselves detected 91% of the high-risk cancers identified by both techniques combined. But they also made some incorrect calls: 123 men classified by MRI-targeted biopsies as having low-risk prostate cancer actually had intermediate-risk disease. And 41 men classified by the MRI approach as having low- or intermediate-risk tumors actually had high-risk cancer.
The investigators emphasized these figures in their conclusion. The combined biopsy, they wrote, “has high predictive value… reduces the likelihood of misdiagnosis, and should translate to decreased diagnostic uncertainty.”
“This is an important study, as it adds significantly to the ongoing evolution of identifying the roles and limitations of traditional systematic biopsies, MRI-targeted biopsies, and the combination of both,” says Dr. Marc Garnick, Gorman Brothers Professor of Medicine at Harvard Medical School and Beth Israel Deaconess Medical Center, and editor in chief of HarvardProstateKnowledge.org. “Again, as with many ultra-sophisticated technologies, significant training and expertise is needed in both the actual performance of the MRI-targeted biopsy itself and its interpretation.”
