A single exhaled breath contains hundreds, if not thousands, of volatile organic compounds (VOCs), some of which may be specific biomarkers of disease. Numerous researchers are now exploring this possibility in the hopes of developing non-invasive, easy-to-use, and cost-effective point-of-care (POC) breath tests that rapidly detect a variety of diseases.
In recent years, breath test researchers have reported several significant findings. For example, Hossam Haick, PhD, a professor of chemical engineering at Technion–Israel Institute of Technology in Haifa, identified a distinctive “breath print” for gastric cancer, and demonstrated that a nanoarray apparatus he and his colleagues are developing accurately discriminates between both gastric cancer patients and control subjects, as well as high- and low-risk premalignant lesions.
Similarly, Michael Phillips, MD, founder and CEO of Menssana Research in Newark, New Jersey, has provided evidence that Menssana’s rapid POC breath test (BreathLink) accurately identifies women with breast cancer, and distinguishes women who have abnormal mammograms from those with normal results. Philips and his colleagues also reported that BreathLink accurately identifies subjects with active pulmonary tuberculosis (TB), and they are collaborating with Colorado State University (CSU) researcher Diane Ordway, PhD, to develop a breath test that detects early TB infection.
“One of the most significant challenges in controlling the spread of TB is early diagnosis,” said Ordway, an assistant professor in CSU’s Mycobacteria Research Laboratory. “Despite decades of effort, no progress has been made in developing validated biomarkers, or measurable indicators, for identifying initial TB infection and the progression of infection to early disease.” The joint effort so far has reported detecting early TB infection in animal models. In another line of research, Australian investigators, including Stephen Trowell, PhD, a senior principal research scientist at the Commonwealth Scientific and Industrial Research Organization in Canberra, identified a specific VOC signature for malaria that was detectable early in infection and correlated with infection severity.
Significant progress also has been reported with breath tests that detect heart and liver disease. For example, Raed Dweik, MD, director of the pulmonary vascular program in the department of pulmonary and critical care medicine at Cleveland Clinic and associate professor of medicine at Case Western Reserve University Lerner College of Medicine, published evidence that acute decompensated heart failure has a unique breath print that distinguished patients with this disease from control subjects. On the liver disease front, Margaret O’Hara, PhD, and Christopher Mayhew, PhD, both of the University of Birmingham, U.K., confirmed the presence of limonene in individuals with liver cirrhosis, and provided evidence that it is a viable biomarker for assessing liver function.
Breath tests also show promise in therapeutic drug monitoring and precision medicine. For instance, Anil Modak, PhD, associate director of medical products research and development at Cambridge Isotope Laboratories in Andover, Massachusetts, reported that a phenotype pantoprazole-13C breath test demonstrated phenoconversion in CYP2C19 enzyme activity in individuals receiving omeprazole and esomeprazole, and that a 13C-dextromethorphan breath test measuring CYP2D6 enzyme activity is being evaluated as a predictor of individual tamoxifen pharmacokinetics. In addition, Modak demonstrated that an L-DOPA-13C breath test is a viable means of evaluating dopa decarboxylase activity and personalizing carbidopa dosages in Parkinson’s disease patients.
The Pathway Forward
These promising, albeit preliminary, findings reflect the potential and scope of breath testing. However, they also offer a glimpse down the long road ahead before this modality becomes a routine part of clinical diagnostics. Study design, methods, and analysis are slowly becoming more rigorous, and greater emphasis is being placed on validating putative breath markers. Both trends are necessary for the field to move forward, and are helping unravel apparent contradictions and inconsistencies in the literature about the identity of reported markers, experts said.
Breath testing research also is following the general in vitro diagnostics trend towards miniaturization and POC testing. For instance, Haick’s team is developing a nanoarray apparatus for the diagnosis of gastric cancer. Similarly, Dweik and his colleagues are trying to miniaturize sensors that can be used in POC testing like breathalyzers are used for detecting alcohol consumption. Researchers are also envisioning ways to expand the utility of breath tests. “There are more things we can do with the breath test than diagnosis,” Dweik observed. “I see how breath testing as it evolves will be used for screening, diagnosis, follow-up, and monitoring.”
The Here and Now
Even as breath testing remains on the verge of rather than fully in the mix of clinical diagnostics, the field nonetheless boasts a robust research enterprise and an influx of young investigators. Veteran researchers attribute this growth to several factors, including technological advances. “One of the things making [the field] boom has been the proliferation of new technologies such as electronic noses,” said Phillips. Dweik observed that another driving force is the exploration of new clinical applications of breath testing. “We are starting to look at areas that previously I would not have thought breath would be a good place to look … but now I’m convinced that more and more they are,” he said.
There also has been an evolution in clinicians’ interest in the modality. As Ordway explained, this may be particularly true for diseases like TB that are endemic to resource-poor regions of the world. “In the tuberculosis field, people are really willing to try new breath tests,” she observed.
Unfortunately, enthusiasm within the field isn’t necessarily translating into financial support. “Not many funding sources are particularly open to breath testing,” said O’Hara. “They don’t think it’s feasible and aren’t willing to take the journey to find out.” Clearly, without adequate funding, progress toward clinical breath tests will be slowed. That said, breath testing is on the agenda for at least some funders. For example, Ordway in April 2014 received a $244,000 grant from the Bill and Melinda Gates Foundation in support of her project.
A Peek Ahead
Given the challenges in identifying and validating VOCs that uniquely identify a particular disease, clinically viable breath tests could be a ways down the road. Philips suggested that some areas are likely to produce new tests sooner than others. “Cancers and infectious diseases are the two hottest areas where we’re likely to see Food and Drug Administration approvals first,” he said.
Meanwhile Haick, Ordway, and Trowell all remain optimistic that their respective lines of research will bear fruit. While Haick believes a test for detecting gastric cancer and premalignant lesions will be available for clinical use within about 5 years, Trumbell predicts that that same length of time “is probably the earliest we could see [a malaria breath test] in the clinic.” In contrast, Ordway, while “extremely hopeful” that a TB field test can be developed, said, “There’s a long way to go from here to getting a [TB test] that’s like a field sobriety breathalyzer test.”
Other promising tests with demonstrated proof-of-concept, such as Modak’s pioneering 13C-labeled enzyme tests, are languishing in the chasm between research and development for want of funding.
Moving Breath Tests Into the Clinic
With the ups and downs of identifying and validating biomarkers, advancing technology, and securing financial support, what will it take to move breath tests into clinical practice? Experts concur that the tests must be simple, fast, insensitive to confounding factors, and provide information and benefits beyond tests currently in use. And, of course, they must be cost effective.
Good collaborations between researchers—and among researchers and clinicians—are also necessary to bring breath tests into the clinic. Understanding cultural differences in openness to new technologies is also important. “A lot of cultural things can impact whether a new technology is accepted or not by the individual,” Ordway noted. As such, the adoption of tests intended for use in less developed areas of the world will depend in part on understanding region-specific cultural issues.
With so many factors to consider, it’s important that the breath testing field stay focused on what matters most to the people it serves. As Dweik put it, “The challenge for people like me and others in the field is to find something that really adds value to the patient and clinician.”
Curtis Balmer, PhD, is a freelance science writer in Potomac Falls, Virginia. +Email: [email protected]