mpMRI accurately detects significant prostate cancer
Overdetection of Insignificant Prostate Cancer
One of the problems with the conventional 12-core TRUS biopsy (transrectal guided ultrasound) has to do with the array of needle placement. It tends to miss cancers in two instances: a) cancers located in the anterior (front) zone of the prostate are easily missed, and b) tumors that have developed in very large glands. While the first instance has to do with geography, the second has to do with probability—the odds of finding a tumor using the same number of needles diminish as the size of the gland increases.
But there’s another often-overlooked problem with 12-core TRUS biopsies. When one or more of the needles contains low-grade cancer, the tumor itself may be insignificant, meaning it may be safely monitored while delaying a treatment decision. This is referred to as overdetection or overdiagnosis. Here is a sobering thought: during the last two decades there were countless men who probably qualified for active surveillance but were sent for whole-gland treatments (surgery or radiation) and now live with urinary or sexual problems as a result.
One way to demonstrate that TRUS biopsy is overdetecting cancer is to compare it with biopsies guided by 3T multiparametric MRI. Ultrasound cannot distinguish tissue differences between cancer and healthy tissue, whereas 3T mpMRI selectively detects more significant cancers, the ones that are potentially dangerous and require biopsy. This is why MRI-guided biopsies are targeted to the actual areas of suspicion revealed by the scan. When comparing TRUS vs. MR guided biopsies, MRI-targeted biopsy generally shows actual cancer in fewer men overall—but the number of significant cancers found is roughly the same between TRUS and MR biopsies. Put another way, MRI-biopsy “ignores” the insignificant cancers that are picked up more frequently by randomized 12-core biopsies.
Regarding all those patients whose insignificant cancer was overtreated after being found by TRUS biopsy, some might argue that since more sophisticated diagnostic methods (biomarkers, 3T mpMRI, genomics) were not yet developed, it was better to be safe than sorry. Fair enough, as long as we’re sure that patients who were left with the long term side effects have no regrets.
Today there is little excuse for overdetection—and therefore overtreatment—of insignificant prostate cancer. In addition to multiparametric MRI, we now have improved blood and urine biomarkers. When these are added to imaging results, we can determine whether a patient should undergo a targeted biopsy. When added to genomics to identify the aggression of the cell line, the doctor and patient can have a high degree of confidence whether the best treatment strategy is focal treatment, radical treatment, or active surveillance.
It is to be hoped that, with the tools we now have, overdetection of insignificant prostate cancer will very soon be a closed chapter in the history of the disease.
- Prostate imaging