Prostate cancer is screened for by digital rectal examination and by measuring serum prostate-specific antigen (PSA) levels. If these arouse any suspicion of prostate cancer, a prostate biopsy is usually recommended.
Prostate biopsies are carried out in several different ways. The most commonly employed techniques are transrectal ultrasound (TRUS) guided systematic biopsy of the prostate, transurethral biopsy and transperienal prostate biopsy.
Transrectal ultrasound (TRUS)-guided systematic biopsy of the prostate
TRUS-guided systematic biopsy of the prostate is considered to be the gold standard for the diagnosis of prostate cancer. The procedure may be done after sedation in most cases. The patient is asked to lie on the left side with the knees slightly drawn up, which relaxes and exposes the rectum. In this left lateral position, the doctor inserts an ultrasound probe into the rectum. The probe is only as thick as an ordinary pencil, and does not cause more than slight discomfort or pressure.
Using the probe, the doctor obtains images of the prostate. This guidance enables the injection of a local anesthetic (usually 1-2% lidocaine) into the area around the prostate, to numb it by nerve. The needle may cause some pain, while the anesthetic produces a brief burning sensation, followed by numbness.
Still under ultrasound guidance, the doctor inserts an 18-gauge needle into several areas of the prostate to recover tissue samples from 10-18 areas. These are prepared for histologic examination. In the standard systematic biopsy, cores of tissue are taken from 12 sites. However, most of these are from the posterior part of the prostate. The anterior tumor foci are often not picked up because of the length of the needle (17 mm) which limits penetration into this part of the gland.
In about 10-20 minutes the patient is ready to leave the biopsy room. The greatest controversy surrounding this procedure has to do with its low sensitivity and the false-negative rate, which has been reported to be up to 20-30%.
Transurethral biopsy
Transurethral biopsy is a method that is used less often, but involves the insertion of a cystoscope. This is a flexible tube with a camera mounted on the end. This is passed through the urethra and tissue samples are recovered from the prostate through the urethral wall.
Transperineal prostate biopsy
The transperineal biopsy (TPB) using points mapped to a brachytherapy template grid is becoming popular because of the better opportunity it offers to sample the prostate in a systematic manner. It especially adds to the accuracy of sampling of the anterior and transition zones, which often contain tumor foci that make up 25–55% of prostate cancer cases. These are the areas that are most often missed by TRUS biopsy. In addition, diagnosed cancers have been upgraded, or new cancer foci detected, in 26–36% of patients who have had a transperineal biopsy, after a prior TRUS biopsy.
In this mode, the patient lies on a special table with the legs positioned in the dorsal lithotomy position, to achieve maximum exposure of the perineal region. Nerve block anesthesia is administered in the area around the prostate and over the perineum (a region that separates the scrotum from the rectal opening), where a small incision is to be made.
A slim ultrasound probe is inserted into the rectum and the prostate volume is assessed. Through the incision, a device bearing a spring-loaded 18-gauge biopsy needle is then used to insert the needle into the prostate. A coaxial needle may be used to prevent the need for multiple perineal skin punctures. Alternatively, a fan-shaped approach is used to take samples from multiple sites using the same entry point.
In second biopsies, a mapping, or stereotactic, or brachytherapy template grid is often used to recover tissue for examination. The needle is inserted at the points on the template (24-38 points), based on the ultrasound image. In general, 20 cores are taken from both sides of the prostate covering all the zones. Each insertion of the needle may produce a very brief but sharp pain.
Currently, a transperineal template or saturation biopsy, as it is called, is suggested only if a previous transrectal ultrasound-guided biopsy has been negative but suspicion of prostate cancer is still high. Spinal or general anesthesia is sometimes recommended in these patients in order to achieve adequate analgesia while taking so high a number of tissue samples.
Advantages
The transrectal route of prostate biopsy may yield false-negatives to the extent of 20-30%. Many of these tumors are picked up by transperineal biopsy, and are situated in the anterior part of the prostate. This method allows better access to this part of the prostate, and thus increases the detection rate. The technique can be used even if the patient does not have a patent anus, due to prior surgery for rectal cancer.
There is a lower risk of major infection as the needle does not have to traverse the rectum on its way to the prostate. Thus the transperineal biopsy is often preferred for patients who are at a higher risk for post-biopsy infectious complications.
MRI-guided prostate biopsy (multiparametric MRI, mpMRI)
Recently techniques which fuse magnetic resonance imaging (MRI) with ultrasound are being introduced to achieve targeted prostate biopsy instead of blind systematic biopsies. This technology allows doctors to map, locate and track the biopsy sites.
The technique is also claimed to allow more accurate diagnosis with higher detection rates, using fewer biopsies. It can pick up cancers with a Gleason score of 7 or above, and it is also better at detecting anterior tumors missed by a TRUS systematic biopsy. It is especially useful in patients undergoing repeat biopsies, with a 41% pick-up rate of cancers on mpMRI-guided biopsies, and with 87% of these being of clinical importance.
What is also important is that lesions detected on mpMRI are also more likely to be aggressive. Thus the technique is of importance in achieving greater detection on repeat biopsies of the prostate in the face of persistent indications for biopsy.
Further Reading