Web Date: March 13, 2013
Mass Spectrometry Detects Cancer Biomarkers In The Chemical Cloud Hovering Over Urine Samples
Urine tests can help doctors diagnose a wide range of diseases, such as bladder infections and diabetes. Cancer may be next. Researchers report a chemical signature linked to gastroesophageal cancers in the plume of volatile organic compounds floating above a urine sample (Anal. Chem., DOI: 10.1021/ac4000656). Looking for the urine chemicals may someday help doctors detect these deadly cancers in their early stages.
Only 20% of people with cancers of the stomach or esophagus receive treatment because the diagnosis often comes too late for doctors to stop the cancer. Also patients don’t usually experience symptoms until the cancer is advanced. “They have a very poor prognosis,” says George B. Hanna of Imperial College London. “There is a need for diagnostic tests that would be able to screen patients” to catch the disease earlier, he adds.
Hanna’s lab uses mass spectrometry to analyze volatile compounds wafting off biological samples in hopes of finding diagnostic chemical signals. This cloud of chemicals is called the headspace of a sample. The team recently found high levels of several compounds, including formaldehyde and hexanoic acid, hovering over gastric juices from people with gastroesophageal cancers. Unfortunately, scanning gastric juices doesn’t make for a good diagnostic screen, Hanna says: Obtaining the fluids from a patient is invasive and yields small volumes. Urine, on the other hand, is plentiful and easy to come by, making it ideal for clinical tests, he says.
To see if they could find the cancer-linked compounds in the headspace of urine samples, Hanna and his team obtained samples from three groups of patients: 17 patients diagnosed with gastroesophageal cancer, 13 people with healthy guts, and 14 patients with noncancer stomach conditions. The researchers transferred 10 mL of each urine sample into a specimen cup and sealed it. They then punctured the seal with a hypodermic needle attached to a tube that fed gaseous samples directly into a mass spectrometer.
When the scientists compared the concentrations of chemicals in the urine headspace of samples from cancer patients to those from people without cancer, they found significant differences in seven compounds. For example, levels of acetylaldehyde and hydrogen sulfide were greater in samples from cancer patients than in those from cancer-free people. These two compounds have been linked to gastroesophageal cancer in other studies in the literature, Hanna says. Using a statistical method, Hanna’s team found that they could use the concentrations of six of the seven chemicals to reliably distinguish between people with gastroesophageal cancers and those without.
Using the volatile part of urine to diagnose cancer is novel and interesting, says Robert H. Weiss of the University of California, Davis. He wonders whether the method will only work for gastroesophageal cancers or if it could be a general cancer detection method. Hanna says that he doesn’t know yet whether the signals are specific to these cancers, but plans to next look at volatile compounds from the urine of people with colon cancer.
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