Early Detection of Prostate Cancer
/ Article By Inês Viana do Carmo, graduating student in Biomedical Sciences, Portugal /
There has been a lot of controversy surrounding prostate cancer screening: and with the most recent discoveries, the discussion will probably heat up again.
Many men tremble upon hearing the words “prostate cancer” coming out of their urologist’s mouth – prostate cancer is the sixth leading cause of death among men worldwide, and so, such diagnosis is never uplifting news. You see, prostate cancer is a rather heterogeneous disease: it always starts with no symptoms at all, but can either have a slow progression, turning out to be in its harmless form – benign prostatic hyperplasia – or become lethal and metastize quickly, with the symptoms only appearing on the later stages, where the chances of survival have already dropped to a mere 30%.
Therefore, screening the male population for the risk of developing this type of cancer is crucial, and currently there are two methods available for detection – prostate specific antigen (PSA) screening and digital rectal examination (DGE).
DGE is a physical exam, where the doctor inserts a gloved and lubricated finger in the man’s rectum to feel the contours of the prostate. DGE only detects morphologic irregularities, providing a limited diagnosis capacity.
As for PSA screening, a blood sample is collected and screened for the exact amount of prostate specific antigen. PSA is secreted by prostatic epithelial cells in order to liquefy semen and allow spermatozoids to swim freely; but you can also detect a small amount in the blood. An elevated count of PSA on a given sample indicates the presence, or a heightened risk, of prostate cancer.
PSA has always been an imperfect biomarker, as it is not cancer specific. There are other pathologies responsible for an increase in this particular antigen’s levels – prostatistis, an infection in prostatic cells, can easily raise the count over 4 ng\mL of blood, the normal level. Ejaculation or testosterone raising medications also have the same misleading effect.
The point is: the reliability of this tests is low when performed individually, and even when used concurrently, the diagnosis is only official through an often uncomfortable and painful biopsy. Although the introduction of this screening methods resulted in a reduction of 37% on mortality rates among patients with prostate cancer (European Journal of Cancer, 2009), we are not benefitting from all these precautions. According to Cancer Research UK, about 66% of the screened population received a false-positive result; additionally, more than 90% of the accurately diagnosed patients presented early-stage (T1 and T2) prostate cancer and underwent unnecessary treatment and procedures to eradicate this condition, as they weren’t really at risk of suffering from the most aggressive stages.
The paradox goes even further as none of these tests ever predicted one’s probability of developing a full-fledged late stage cancer: there are no exclusive molecular markers, there are no particular signs or alterations that might forecast that outcome.
This is where Scott Tomlins, M.D., Ph.D. in Pathology and Urology, and his team at Michigan’s University come in. Inspired by an amazing discovery on the field, Mi-Prostate Score (or MiPS) was created. MiPS is a novel urine test that promises an increase in PSA screening specificity and sensitivity – by incorporating two new cancer-associated markers on the essay’s testing parameters.
The new version not only quantifies PSA levels in urine samples, but also PCA3, a gene overexpressed in cancerous prostatic tissue; and more importantly, T2:ERG – a type of gene fusion between two genes that is believed to cause prostate cancer, described by Arul Chinnaiyan, M.D., Ph.D., in 2005.
Mi-Prostate Score has already been validated by the Michigan’s researchers, and will available for request through you urologist. Albeit the modification is not designed to detect late stage cancer, it now provides an accurate estimate of its possible severity – aiding doctors choose the best diagnostic approach based on the result.
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