Prostate biopsy is currently the only way to definitively diagnose prostate cancer. It is also used to differentiate between cancer and benign prostatic hyperplasia, a common condition in older men. However, after a prostate biopsy, the results may not be conclusive. This is why a repeat biopsy is sometimes necessary, mainly for three different reasons:
- PSA continues to rise after a first negative biopsy.
- The first biopsy showed Atypical Small Acinar Proliferation (lesion suspicious for cancer but not diagnostic) or extensive, high-grade Prostatic Intraepithelial Neoplasia (premalignant lesion).
- The result of the first biopsy was that of a low-risk prostate cancer (small, low-grade tumor located in the prostate) and the urologist decided to include it in an active surveillance program. This means doing new biopsies periodically to make sure that the tumor is still low risk and has not transformed over time into a higher risk tumor.
What are the benefits of MRI-guided biopsy?
Ultrasound and MRI-guided prostate biopsy uses imaging guidance and a needle to remove tissue from the prostate for the purpose of looking for disease. The ultrasound probe used in prostate biopsies is about the size of a finger. Once the probe has been placed in the rectum, the biopsy is performed using a spring-driven core needle biopsy device, or biopsy gun.
MRI is the best test to plan the diagnosis and select patients who are candidates for prostate biopsy, since:
- It indicates whether there are suspicious areas of cancer and their precise location.
- Its images accurately guide us to perform the prostate biopsy by fusion.
- It tells us if there are one or more suspicious areas of cancer and this is important for biopsy and treatment planning.
- It informs us of the degree of aggressiveness of the tumor.
How is MRI-guided biopsy performed?
MRI-guided biopsy can be performed with an endorectal approach or with a transperineal approach.
- For endorectal biopsy, the patient usually lies face down. The biopsy device has a built-in endorectal coil to aid in visualization, and a targeting slot for insertion of the biopsy needle.
- For transperineal biopsy, the patient usually lies on his or her back, and the biopsy is performed with a guidance template placed against the perineum (just below the scrotum).
In what type of patient is it recommended?
The study of the prostate by Magnetic Resonance Imaging (MRI) requires modern MRI equipment (multiprobe) and a radiologist who is an expert in this technique. It is practiced in men with suspected prostate cancer and a study is performed with 3 sequences: T2 planes, axial diffusion and perfusion study.
MRI is very reliable for patients who have already undergone prostate biopsy, the PSA continues to rise and a new biopsy is considered. In these cases MRI allows us to assess whether there are foci-areas suggestive of cancer or whether the prostate is normal. If the MRI identifies areas suggestive of cancer we should perform directed biopsies in this suspicious area marked by the MRI. If the MRI is normal, there are no suspicious areas, the biopsy can be avoided.
Currently, MRI is also very useful in patients with elevated PSA and Normal Rectal Tact, in whom a first biopsy is considered due to high PSA. In these cases, the presence of suspicious areas of cancer in the MRI will indicate the need to perform a prostate biopsy and if the MRI study is normal, without suspicious foci, the biopsy could be avoided.
The PROMIS study (Prostate M R Imaging Study) has investigated whether prostate MRI before biopsy could safely exclude the presence of significant prostate cancer (high grade) and avoid biopsy (Hashim et al). The results showed that MRI is twice as sensitive as classical (ultrasound-guided) biopsy in detecting prostate cancer and allows 27% of patients to avoid prostate biopsy.