Cancer screening is a critical approach for preventing cancer deaths because cases caught early are often more treatable. But while there are already existing ways to screen for different types of cancer, there is a great need for even more safe, cheap and effective methods to save even more lives.
Now a team of researchers led by Shaoxin Li at Guangdong Medical College in China has demonstrated the potential of a new, non-invasive method to screen for prostate cancer, a common type of cancer in men worldwide. They describe their laboratory success testing an existing spectroscopy technique called surface-enhanced Raman scattering (SERS) with a new, sophisticated analysis technique called support vector machine (SVM).
As they described in a new paper in Applied Physics Letters, from AIP Publishing, they combined SERS and SVM and applied them to blood samples collected from 68 healthy volunteers and 93 people who were clinically confirmed to have prostate cancer. They found their technique could identify the cases of cancer with an accuracy of 98.1 percent.
If the technique proves safe and effective in clinical trials, it may become a new method available to patients and their doctors, helping to improve the early detection and diagnosis of this type of cancer, said Li.
“The results demonstrate that label-free serum SERS analysis combined with SVM diagnostic algorithm has great potential for non-invasive prostate cancer screening,” said Li. “Compared to traditional screening methods, this method has the advantages of being non-invasive, highly sensitive and very simple for prostate cancer screening.”
A COMMON CAUSE OF CANCER
According to the World Health Organization, prostate cancer is one of the most common types of cancer in men worldwide and a leading cause of cancer-related death. Every year, there are about 899,000 new cases and 260,000 mortalities, comprising 6 percent of all cancer deaths globally. About 1 in every 6 men will develop prostate cancer over their lifetimes.
Finding prostate cancer early
Screening refers to testing to find a disease such as cancer in people who do not have symptoms of that disease. For some types of cancer, screening can help find cancers at an early stage, when they are more easily cured. The goal of screening is to help people live healthier, longer lives.
The goal of screening for prostate cancer is to find it early, in the hope that it can be treated more effectively.
Prostate cancer can often be found early by testing the amount of prostate-specific antigen (PSA) in a man’s blood. Another way to find prostate cancer early is the digital rectal exam (DRE). For this exam, the doctor puts a gloved finger into the rectum to feel the prostate gland. These 2 tests are described in more detail in the section “What tests can detect prostate cancer?”
If the results of either one of these tests are abnormal, further testing is needed to see if there is a cancer. If prostate cancer is found as a result of screening with the PSA test or DRE, it will probably be at an earlier, more treatable stage than if no screening were done.
Since using early detection tests for prostate cancer became relatively common in the United States (about 1990), the prostate cancer death rate has dropped. But it isn’t clear yet that this drop is a direct result of screening. It could also be caused by something else, like improvements in treatment.
There is no question that screening can help find many prostate cancers early, but there are limits to the prostate cancer screening tests used today. Neither the PSA test nor the DRE is 100% accurate. These tests can sometimes have abnormal results even when a man does not have cancer (known as false-positive results). Normal results can also occur even when a man does have cancer (known as false-negative results). Unclear test results can cause confusion and anxiety. False-positive results can lead some men to have a prostate biopsy (with small risks of pain, infection, and bleeding) when they do not have cancer. And false-negative results can give some men a false sense of security even though they actually have cancer.
Another important issue is that even if screening detects a cancer, doctors often can’t tell if the cancer is truly dangerous. Finding and treating all prostate cancers early might seem as if it would always be a good thing, but some prostate cancers grow so slowly that they would probably never cause problems. Because of an elevated PSA level, some men may be diagnosed with a prostate cancer that they would have never even known about at all. It would never have led to their death, or even caused any symptoms.
While a simple blood test for elevated levels of a protein marker known as prostate specific antigen (PSA) has been used for years to screen for early cases of prostate cancer, the test is far from perfect because the elevated PSA levels can be caused by many things unrelated to cancer. This contributes to over-diagnosis, uncomfortable tissue biopsies and other unnecessary treatment, which can be costly and carry significant side effects. Because of this, the U.S. Preventative Services Task Force now recommends against PSA-based screening for prostate cancer.
According to Li, many scientists have thought about applying SERS to cancer detection because the surface-sensitive type of spectroscopy has been around for years and is sensitive enough to identify key molecules in very low abundance, like pesticide residues on a contaminated surface. This would seem to make it perfect for spotting subtle signals of DNA, proteins or fatty molecules that would mark a case of cancer—exactly why he and his team tackled the problem.
The challenge, he said, was that these changes were, if anything, too subtle. The signal differences between the serum samples taken from the 68 healthy volunteers and the 93 people with prostate cancer were too tiny to detect. So to accurately distinguish between these samples, Li’s group employed a powerful spectral data processing algorithm, support vector machine (SVM), which effectively showed the difference.
While the work is preliminary, it shows that serum SERS spectroscopy combined with SVM diagnostic algorithm has the potential to be a new method for non-invasive prostate cancer screening, Li said. The next research step, he added, is to refine the method and explore whether this method can distinguish cancer staging.
The article, “Noninvasive prostate cancer screening based on serum surface-enhanced Raman spectroscopy and support vector machine,” is authored by Shaoxin Li, Yanjiao Zhang, Junfa Xu, Linfang Li, Qiuyao Zeng, Lin Lin, Zhouyi Guo, Zhiming Liu, Honglian Xiong and Songhao Liu. It appears in the journal Applied Physics Letters on September 2, 2014. After that date, it can be accessed at: http://scitation.aip.org/content/aip/journal/apl/105/9/10.1063/1.4892667
Authors of the paper are affiliated with Guangdong Medical College; Guangdong Provincial Key Laboratory of Medical Molecular Diagnostics, No. 1; Sun Yat-sen University Cancer Center; and South China Normal University.
ABOUT THE JOURNAL
Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology.
Jason Socrates Bardi
American Institute of Physics