TRUS Biopsy: Still Trying to Solve the Riddle

Matt Mullenweg, the originator of the popular open source WordPress software, has been quoted as saying, “Whenever there’s a new form of media, we always think it’s going to replace the old thing, and it never does. We still have radio, however long after TV was introduced.” It can be just as true in medicine. Even when a new test or procedure starts to prove itself, the old things linger on.

In the world of prostate cancer (PCa), a transrectal ultrasound-guided (TRUS) biopsy is considered the diagnostic gold standard among urologists. Much has been written about its imperfections, including:

• It misses cancer upwards of 30% of the time
• It tends to hit some areas more than others
• It over detects low-risk cancer and often fails to pick up high grade cells
• It can be painful
• There’s a risk of urinary, sexual and infection side effects
• If the first biopsy is negative, there’s a high rate of negative repeat biopsies (all missing the same tumor)
• Repeat biopsies leave scars that can confound future MRI scans

I understand how a medical specialty is reluctant to changing a diagnostic test that a doctor can do in his/her office without a substantial capital outlay. But if it’s a “standard” procedure, why there is still uncertainty about the optimum number of needles. Today, 10-12 cores is typical, though transperineal mapping biopsies can average 40+ needles – also guided by ultrasound with its poor discrimination of tissue differences. However, the riddle continues to be asked: what is the ideal number of needle cores?

A recent paper from a Brazilian university medical center is another effort to weigh in. They compared two established biopsy protocol as well as the total number of needles taken during both. They correlated biopsy findings with PSA, prostate volume, Gleason score, and detection of cancer precursors (high grade PIN and ASAP). A total of 351 men with factors suspicious for prostate cancer underwent the study biopsies. They were sedated and anesthetized prior to the procedure. The biopsy was done in 3 stages by starting with a 10 core scheme used by the study center, then a 12 core design (Brazilian Society of Urology) and finally all 16 totaled together (see chart below).

 

No. cores		PCa detection rate
10	5 needles on each side (base, middle third, apex, medial [transitional zone] and latero-lateral)	102 men (29.06%)
12	6 needles on each side (base, middle third, apex, and more lateral regions of the base, middle third, and apex but not right and left medial or right and left latero-lateral)	99 men (28.21%)
16	All cores taken together	107 men (30.48%)

 

None of the differences were statistically significant, nor was there any significant correlation with PSA, gland volume, Gleason score, and presence of PIN or ASAP. The team concluded that 10 cores was sufficient, especially in the light of other considerations of extended biopsies (increased risk of complications, general instead of local anesthesia, longer procedure duration.)

It is personally gratifying to be able to offer patients 3T multiparametric MRI as a way to rule the need for biopsy in or out, and an MRI-guided targeted biopsy as a less invasive and more accurate procedure.

The number of cores depends on what the scans show as suspicious, and we’re far less likely to capture insignificant PCa and highly likely to sample the most aggressive areas within a tumor’s core.

There will always be riddles because of the mystery of the human body and the way disease begins and progresses. But thankfully for our Center, looking to establish a fixed number of biopsy needles for a hit-and-miss procedure is not one of them.