Prostate cancer diagnosis generally occurs after prostate-specific antigen (PSA) testing and digital rectal exam (DRE) have given a man’s physician reason to suspect cancer. While other diagnostic exams may be ordered to help better understand a prostate abnormality, a prostate cancer diagnosis can only be confirmed after biopsy has been performed to remove prostate tissue for testing in a laboratory.
Transrectal ultrasound (TRUS) biopsy has been the traditional method of diagnosing prostate cancer following abnormal DRE and/or PSA testing. However, magnetic resonance imaging (MRI), used with and as an alternative to ultrasound, is emerging as a more accurate method for determining who would benefit from biopsy.
Transrectal Ultrasound Biopsy
TRUS biopsy uses ultrasound to produce images of the prostate gland for the purpose of guiding biopsy needles, which extract prostate tissue samples. Ultrasound may also be used prior to TRUS biopsy to plan for the procedure or better understand a potential abnormality.
During the procedure, a small probe is inserted into the rectum. A biopsy needle attached to the probe is quickly shot into and out of the prostate gland. Generally, 8 to 14 cores, or samples, are removed for testing. Because ultrasound cannot produce detailed images of the prostate gland, particularly certain regions, TRUS biopsy is often referred to as ‘blind’ biopsy. However, TRUS biopsy has been the standard of care in prostate cancer diagnosis for many years and continues to help save lives.
MRI-Guided Biopsy & MRI-TRUS Fusion Biopsy
A specific imaging technique called multiparametric MRI is being used with success in prostate cancer detection and diagnosis. Multiparametric MRI, like transrectal ultrasound, can be used prior to biopsy to investigate for abnormalities and to guide needles during biopsy.
MRI, unlike ultrasound, can produce detailed images of the prostate gland that provide helpful information about the volume of a tumor, the location of a tumor and a tumor’s potential for aggressive growth. Because MRI can view the prostate gland better than ultrasound, only 2 to 4 cores are generally removed during MRI-guided or MRI-TRUS fusion biopsy.
During MRI-guided biopsy, a small probe is inserted into the rectum and real-time MRI images are used to guide a biopsy needle to the specific location of a tumor. During MRI-TRUS fusion biopsy, images previously produced by MRI are used during TRUS biopsy to better guide biopsy needles.
TRUS Biopsy vs. Prostate MRI
For many years, TRUS biopsy has played an instrumental role in prostate cancer diagnosis. However, TRUS biopsy is associated with several disadvantages:
- Up to one-third of cancers missed on initial biopsy.
- Up to one-half of TRUS biopsy samples inappropriately graded due to sampling errors.
- Repeat biopsies necessitated by inaccurate results increases risk for side effects, such as infection.
While there is still a ways to go before prostate MRI and MRI-guided biopsy replace TRUS biopsy, it is emerging as a viable alternative to TRUS. Prostate MRI can:
- Accurately identify or rule out high-grade prostate cancer at rates above 90 percent.
- Estimate the aggressiveness of a prostate cancer with relative accuracy prior to biopsy.
- Guide biopsy needles to precise location of tumors, eliminating the need for repeat procedures and more needles.