Overdetection of Insignificant Prostate Cancer

By: Dan Sperling, MD

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.

One way to demonstrate that TRUS biopsy is overdetecting cancer is to compare it with biopsies guided by 3T multiparametric MRI. Keep in mind that ultrasound cannot distinguish tissue differences between cancer and healthy tissue. On the other hand, 3T mpMRI selectively detects larger and more significant tumors, 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 advanced imaging. When comparing TRUS vs MR guided biopsies, it is safe to say that generally MR-targeted biopsy 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, when MR-biopsy “ignores” the insignificant cancers that are picked up more frequently by randomized 12-core biopsies.

The important implication is that over the last 15 years or so, countless men have been sent for surgery or radiation to treat cancers that may well have qualified the patient for Active Surveillance (AS). Although 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 urinary, sexual and bowel problems as a result of overtreatment have no regrets.

However, today there is little excuse for overdetection—and therefore overtreatment—of insignificant cancers that qualify a patient for AS. Today, in addition to sophisticated imaging, we do 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 (including focal laser ablation), radical treatment, or even no treatment for the time being.

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.

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