Dr. Taneja is one of a growing number of doctors and researchers investigating how MRI scans can be used to help detect and treat prostate cancer more effectively. Proponents of the technique say the system could help resolve some of the problems that plague doctors and prostate-cancer patients, such as telling the difference between aggressive, dangerous cancers and clinically insignificant ones that might not need treatment.
MRI scans also are being tested as a tool to help improve certain treatments for prostate cancer, especially focal therapy, which uses an energy source to destroy small tumors inside the prostate. The procedure mostly leaves the gland intact, avoiding surgical side effects such as sexual dysfunction and incontinence.
Data so far suggest that using MRI-guided biopsies allows doctors to identify a larger percentage of high-grade, aggressive cancers than using conventional biopsies, potentially saving lives, said Dr. Taneja, co-director of the Smilow Comprehensive Prostate Cancer Center at NYU. Still, MRIs miss more tumors overall, although these are mainly small, low-grade cancers, he said.
Dr. Taneja will make the case for the technique in a panel discussion at the Society of Urologic Oncology’s annual meeting in December. The panel will explore the question: Should MRI be the standard of care before biopsy?
Some urologists say MRI-guided biopsies need more conclusive studies to justify the added expense. An MRI can cost between $600 and more than $2,000, although Medicare and many private insurers typically cover some or all of that.
Prostate cancer is among the most common types of cancers in men and the second most deadly, after lung cancer. There are an estimated 233,000 new cases of prostate cancer a year in the U.S. and 29,480 deaths, according to the National Cancer Institute.
Currently, the routine procedure for men getting screened for prostate cancer starts with a PSA, or prostate specific antigen, blood test. If a PSA reading is high, a biopsy is usually performed with needles guided by an ultrasound probe. Ultrasounds can’t visualize the prostate very well so urologists are somewhat randomly sampling the gland. When a biopsy comes up negative, men sometimes have to repeat the procedure.
“The prostate is a walnut-size gland and lesions can be as small as 1 centimeter or less,” said William Dahut, clinical director of the Center for Cancer Research at the National Cancer Institute, which has been using MRI in prostate-cancer research for nearly a decade. “How many times do you need to biopsy a walnut with a small needle before you have the full walnut?”
At centers like NYU and the University of California, Los Angeles, most men will have an MRI before undergoing a biopsy. With the MRI, the institutions use a multiparametric technique that includes measuring blood flow and water movement in the prostate, which can help identify cancer cells. Suspicious areas are identified by a radiologist and rated on a five-point scale reflecting degree of suspicion.
Specialized software is used to build a three-dimensional model of the MRI that can be fused with the ultrasound at the time of biopsy. Robotic spatial tracking allows doctors to align the biopsy needle guide with the MRI.
Because conventional biopsies can’t always distinguish when a cancer is clinically insignificant, patients sometimes undergo unnecessary surgery, radiation or other therapy. Such overtreatment has been a concern in the medical community for some time.
“We’ve postulated that [MRI] imaging can correct all of those problems,” said Dr. Taneja. “The cancers we primarily miss when we do the targeted biopsy tend to be the smaller, low-grade cancers that we think are randomly found on routine biopsies,” he said.
More doctors have been including MRIs in their diagnoses, although the technique isn’t without controversy. Some urologists say comparing detection rates of different types of biopsy procedures is difficult because missed cancers aren’t always later discovered. There is also disagreement on when to consider a cancer aggressive. Many urologists, including Dr. Taneja, say a high-grade, aggressive tumor is one that ranks 7 or higher on the Gleason scale, a commonly used measure to classify a cancer’s aggressiveness based on a pattern of abnormal cells. Some urologists say a score of 6 or higher is sufficiently aggressive to warrant treatment. Gleason scores can be between 2 and 10, but most early-stage prostate cancers have a score of 6 or higher.
Leonard S. Marks, a professor of urology at UCLA School of Medicine, also routinely uses MRI on prostate-cancer patients. Since 2009, he and colleagues have conducted about 1,400 MRI-fusion biopsies in 1,100 men. In a study published last year in the Journal of Urology, the researchers found that MRI-guided biopsies were three times as likely to identify cancer compared with a conventional biopsy. Another finding: 38% of the men with high-grade cancer had disease detected only when MRI was used.
“Over and over again we see cancers that have been missed by conventional biopsy that are detected by targeted fusion biopsies,” said Dr. Marks.
Still, Dr. Marks said his data find that about 20% of MRI scans which appear to be normal end up having a serious but treatable cancer. The interpretation of a prostate MRI can be difficult, he said. “It takes a number of years for a radiologist specializing in MRI of the prostate to be able to read these images correctly,” he said.
Dr. Dahut of the National Cancer Institute said MRI scans may be most useful for selecting and monitoring patients with low-grade cancers. They are also helpful in detecting or excluding significant disease in patients who have elevated PSA levels and have had multiple negative biopsies, he said.
“Improved imaging with MRI may allow one to confidently recommend surveillance to a greater number of patients and to discover aggressive disease in areas that are not usually biopsied,” Dr. Dahut said. “No technology is perfect, that’s for sure. However, it is clear that our tools and ability to use these tools continues to markedly improve,” he said.
