How is prostate cancer diagnosed?
As prostate cancer typically affects the peripheral zone (outer part) of the prostate gland, it does not typically cause voiding symptoms until it is advanced. Men are therefore more likely to be diagnosed with prostate cancer if they have undergone a digital rectal examination and/or a PSA test by their General Practitioner or Urologist.
A digital rectal examination (DRE) involves passing a lubricated gloved finger into the rectum (back passage). The prostate is located just in front of the rectum, and so a DRE assesses the posterior (back) part of the prostate. A DRE can give an estimate of the size of the prostate and also indicate whether there are any irregularities in the prostate gland (e.g. nodules). Not all prostate cancers though can be felt on DRE. A small percentage of prostate cancers do not secrete PSA, and so a DRE is an important part of detecting some prostate cancers. A DRE is useful in staging prostate cancer. When a tumour cannot be felt it is classified as a T1 tumour. When a nodule is felt, but does not appear to spread beyond the prostate capsule, it is a T2 tumour. A T3 tumour is where cancer has spread outside the prostate into the surrounding tissues. Advanced T4 prostate cancer is cancer that has spread into surrounding organs such as the bladder or rectum.
PSA stands for Prostate Specific Antigen. This is a protein produced by the prostate gland that is present in the ejaculate fluid. It prevents semen from becoming too thick, and it therefore assists with fertilisation after intercourse. A small amount of PSA is also present in the blood stream.
Whilst the PSA blood test is not an ideal screening test for prostate cancer, it is helpful in determining the chance that a male patient has prostate cancer. It can also be used to determine which treatment option is likely to benefit a patient, and it can also help monitor cancer progress following treatment. PSA is secreted in elevated amounts in the blood stream in patients with prostate cancer, but other conditions can also cause an increased PSA such as BPH, a urinary tract infection, prostatitis and prostate manipulation (e.g. following a urethral catheter insertion or a DRE).
Whilst there is no screening for prostate cancer in Australia, it is recommended by the Urological Society of Australia and New Zealand that men have a PSA test at the age of forty to act as a baseline level and to also determine the future risk of developing prostate cancer.
If a clinical suspicion of prostate cancer is present, based on an abnormal digital rectal examination or elevated PSA, a prostate biopsy will likely be required. A biopsy involves the passage of a small needle into the prostate gland, with small cores of prostate tissue removed and then examined under a microscopic by a Pathologist following the procedure. Occasionally though prostate cancer can be diagnosed following a transurethral resection of the prostate (TURP) ie: in the prostate chips removed. A biopsy can be done three different ways:
Transrectal ultrasound (TRUS) guided prostate biopsies – this procedure is usually done under sedation or occasionally under local anaesthesia. An ultrasound probe is inserted into the rectum to visualize the prostate, and a needle is passed through the rectum and into the prostate (typically twelve biopsy cores are taken). This procedure mostly biopsies the posterior part (peripheral zone) of the prostate. The risks include bleeding (blood in the ejaculate, urine or rectum), infection/sepsis, failure to diagnose cancer (especially if there is a central or anterior tumour) and temporary urinary retention.
Transperineal prostate biopsies – This procedure is done under a general anaesthetic. An ultrasound probe is inserted into the rectum to visualize the prostate, but the needle biopsies pass through the perineum (the area between the anus and scrotum) and into the prostate. Either a small number of targeted biopsies or saturation prostate biopsies can be performed with this approach. The advantage of transperineal biopsies are that the anterior and central parts of the prostate are better sampled, and there is a lower risk of infection as the skin of the perineum can be disinfected prior to passage of the biopsy needle. The risk of rectal bleeding is very low as the biopsies are not passed through the rectal wall. Because some of the needles are passed close to the urethra there is a slightly higher risk of haematuria (blood in the urine) and temporary voiding difficulties.
MRI guided biopsies – In the event that a small lesion is found on 3T multiparametric MRI scanning (e.g. < 5mm) MRI guided biopsies (typically two cores) can be taken. This ensures that the abnormal area has been sampled. The procedure can be done with sedation. As the biopsy needles are passed through the rectal wall into the prostate, there is a risk of infection/sepsis and bleeding. One of the possible downsides of MRI guided biopsies is that other areas of the prostate gland are not sampled and some significant tumours that are not identified on the 3T multiparametric MRI scan may be missed.
Once the tissue has been removed and examined by the Pathologist, a grade can be applied to the tumour. The grade is a measure of how aggressive the prostate cancer is, and may indicate how quickly the cancer will grow and spread. The grade of cancer is better known as the Gleason score. The score can range between 2 and 10, with the lowest Gleason score typically seen on prostate biopsies being 6. A Gleason score of 6 (or less) is typically a low risk tumour, whereas a Gleason 7 cancer indicates a medium risk cancer, and a score of 8-10 indicates a high grade cancer.
3T Multiparametric MRI scans:
Advancement in MRI imaging has led to increased accuracy in diagnosing prostate cancer. A 3T multiparametric MRI scan is helpful in identifying the position of cancer in the prostate and therefore aid in the accuracy of subsequent biopsies. In particular anterior tumours and central tumours, which have a higher chance of being missed with TRUS biopsies, can be identified. Whilst very helpful in identifying prostate cancers, and avoiding the need for prostate biopsies in some patients, these scans are not 100% accurate. 3T multiparametric MRI scans have up to a 90% chance of diagnosing significant prostate cancers. A negative MRI scan therefore does not completely exclude prostate cancer, and subsequent Urological follow-up is recommended with a negative MRI scan. At the present time MRI scans are not subsidised, and the cost can range from ~$550 to $600. It is important that 3T multiparametric MRI scans are done at an appropriate radiological centre, utilising the correct software. The images also should be reviewed by an experienced Radiologist/Urologist.