The latest results from their experimental chemical odor test show that 90 percent of urine samples from men with prostate cancer contained a small set of identifiable volatile compounds that were absent in samples from healthy men.
The findings feature at this year's spring national meeting of the American Chemical Society in San Francisco, CA.
After skin cancer, prostate cancer is the most common cancer in men in the United States, where around 1 out of every 7 men can expect to be diagnosed with the disease during their lifetime.
The cancer begins in cells of the prostate - a male gland that makes a thick fluid that is added to semen and is situated in front of the rectum and below the bladder.
Semen and urine travel through the center of the prostate (using a tube called the urethra) to exit the body via the penis. Some of the urinary and sexual symptoms of prostate cancer - and noncancerous conditions such as inflamed and enlarged prostate - arise because the swollen gland squeezes this channel.
While early detection is one of the most important factors in helping men to survive prostate cancer, diagnosis is not straightforward. It usually relies on a combination of a digital rectal exam and a blood test to measure prostate-specific antigen (PSA) to help decide whether a biopsy should be done.
Alternative to biopsies needed
However, biopsies are expensive, uncomfortable, and carry the risk of infection. Unfortunately, thousands of men undergo the procedure - which involves inserting a needle into the prostate gland to remove pieces of tissue for analysis - only to discover that they do not require cancer treatment.
Fast facts about prostate cancer
- There are currently more than 2.9 million prostate cancer survivors living in the U.S.
- The average age of diagnosis is 66 years.
- The disease is rarely diagnosed before the age of 40.
One of the causes of unnecessary biopsies for prostate cancer diagnosis is that other conditions - such as a prostate infection - can also give high PSA levels. Consequently, the PSA test is widely recognized as unreliable, and so biopsies are performed in order to get a clearer answer.
Scientists are therefore investigating various alternative ways to improve prostate cancer diagnosis without having to rely on biopsies.
One approach has been inspired by studies that show that dogs can detect volatile organic compounds in the urine of men with prostate cancer. One such study showed that the animals could sniff out prostate cancer with 98 percent accuracy.
The researchers behind the new study believe that they have identified the molecules that likely give the urine of men with prostate cancer its unique scent, and they have developed a chemical sniff test to detect them.
Senior investigator Prof. Mangilal Agarwal, an associate director of research and development at Indiana University-Purdue University Indianapolis, has been developing a sensor to detect hypoglycemia (low blood sugar) in human breath.
He and his colleagues - including Dr. Amanda Siegel, co-presenter of the study results - were inspired by the success of the dog studies and decided to investigate which molecules might be involved. "If dogs can smell prostate cancer, we should be able to, too," says Dr. Siegel.
Volatile compounds unique to prostate cancer urine
For their study, the team tested urine samples collected from 100 men who were undergoing prostate biopsies.
The researchers noted that some previous studies had experienced problems with chemical degradation. Thus, to better preserve the samples during analysis, they added sodium chloride and neutralized their pH.
Using gas chromatography-mass spectrometry to analyze the volatile organic compounds in the air above the urine samples, the team found a set of small molecules that appear to be unique to prostate cancer.
The molecules were present in 90 percent of samples from men who were subsequently found to have prostate cancer, but they were not present in samples from men who did not have it.
The researchers are already planning to validate their findings with a large-scale study involving several health centers. They also hope to compare their findings with results obtained from dogs, with the help of a local dog trainer.
They suggest, if these further tests confirm their findings, that their chemical sniff test will be available for clinical use within the next few years.
Currently, around 60 percent of men who have biopsies to detect prostate cancer do not need one, say the researchers.
"We hope our research will help doctors and patients make better-informed decisions about whether to have a biopsy, and to avoid unwarranted procedures."
Dr. Amanda Siegel