New blood test for prostate cancer avoids false positives
A newly developed blood test has been found to efficiently and accurately detect the presence of aggressive prostate cancer, which could help men avoid unnecessary and invasive biopsies, over-diagnosis and overtreatment.
Prostate cancer is the most common cancer in Western men, with 1.3 million new cases diagnosed each year worldwide. It is currently detected using a blood test that measures prostate specific antigen (PSA) levels — but although the PSA test provides early diagnosis, it also has a high number of false positives.
When a high PSA level in the blood is detected, the patient undergoes a tissue biopsy of the prostate gland, which is invasive and carries a significant risk of bleeding and infection. About 75% of all PSA positive results end up with negative biopsies that do not find cancer, and most diagnosed early-stage prostate cancers are not fatal if left untreated. The current practice therefore results in unnecessary biopsies, over-diagnosis and overtreatment in many men.
In contrast to the current method, the Parsortix prostate cancer test from diagnostics company ANGLE detects early cancer cells, or circulating tumour cells (CTCs), that have left the original tumour and entered the bloodstream prior to spreading around the body. By measuring intact living cancer cells in the patient’s blood, rather than the PSA protein which may be present in the blood for reasons other than cancer, it potentially provides a more accurate test for prostate cancer. This is what UK researchers, led by Queen Mary University of London, set out to determine.
The researchers looked at the use of the CTC test in 98 pre-biopsy patients and 155 newly diagnosed prostate cancer patients enrolled at St Bartholomew’s Hospital in London. They found that the presence of CTCs in pre-biopsy blood samples were indicative of the presence of aggressive prostate cancer, and efficiently and non-invasively predicted the later outcome of biopsy results.
When the CTC test was used in combination with the current PSA test, it was able to predict the presence of aggressive prostate cancer in subsequent biopsies with over 90% accuracy — said to be better than any previously reported biomarkers. Additionally, the number and type of CTCs present in the blood was also indicative of the aggressiveness of the cancer.
“Testing for circulating tumour cells is efficient, non-invasive and potentially accurate, and we’ve now demonstrated its potential to improve the current standard of care,” said lead researcher Professor Yong-Jie Lu, from Queen Mary’s Barts Cancer Institute. “By combining the new CTC analysis with the current PSA test, we were able to detect prostate cancer with the highest level of accuracy ever seen in any biomarker test, which could spare many patients unnecessary biopsies. This could lead to a paradigm shift in the way we diagnose prostate cancer.”
The results of the study, published in the Journal of Urology, need to be further validated in other independent research centres before the CTC test is available either privately or on the NHS in the UK, which could take a further 3–5 years. Clearance by the US FDA could also take 3–5 years.
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