Novel Colorectal Cancer Detection Through Exhaled Breath

Many of us would be familiar with the breathalyzer test that is commonly used to estimate a person’s blood alcohol content. Soon, in somewhat similar yet different circumstances, our exhaled breath may be used to detect the presence of colorectal cancer in our body.

Will a new colorectal cancer breath test also detect alcohol in the blood? Not quite. The breath test will detect other volatile organic compounds (VOCs) that are released as a result of certain cancer-related metabolic processes, and this could potentially help triage patients who present preliminary symptoms of colorectal cancer and direct them for more comprehensive screening tests like a colonoscopy.

Volatile organic compounds, or VOCs, are gaseous metabolites that result from metabolic alterations caused by cancer tissue. These carbon-based byproducts are transported via the blood to the alveoli of the lungs, where it is released through the exhaled breath. These VOCs are also often present in other body media including the blood, urine and stool.

VOCs can result from different sources; exogenous VOCs originate from the external environment, such as a person’s diet or smoking habits. Endogenous VOCs, on the other hand, are the end-result of human or microbial metabolic processes in the colon.

The production of VOCs in the large intestine is about as heterogeneous as the causes of colorectal cancer themselves, and remains a process that requires clarity. The extent to which diet, the gut microbiota as well as other carcinogens from smoking and the metabolism of alcohol play a role in the production of VOCs is still not well studied.

Nonetheless, VOCs are considered a biomarker of growing importance as a means of studying the metabolic state of an organism. The VOCs detected are reflective of the biochemical reactions caused by biological activities like apoptosis/programmed cell death, oxidative stress or inflammation, and disease-related VOCs may be part of a cascade of reactions as the body attempts to respond to those biological activities.

An important caveat to note, however, is that VOCs can result from cancer-related biological activities, and some of these are not specific to just one type of cancer. Through analysis of VOC-related studies, Janfaza and team mapped out the different VOCs and the cancers they are most associated with.

While the majority of the VOCs so far are linked with lung and other cancers, there remains a few unique VOCs that are specific to colorectal cancer, and can act as a unique biomarker for the disease.

Given that the colorectal cancer breath test is still a work-in-progress and novel detection method, the best and exact ways in which breath samples are collected are still being developed.

However, the collected samples can be analyzed for various VOCs using either gas chromatography-mass spectrometry (GC-MS), which first separates the components of exhaled breath — including carbon dioxide, water vapor, oxygen and VOCs — before measuring the mass-to-charge ratio of the ions present in the components.

Alternatively, an electronic nose (or e-nose) consists of a three-part system that first collects the sample, detects the components in the sample, and computes and analyzes the results. The e-nose is modeled after — you guessed it — the human nose and olfactory system, and aims to reproduce the capability of the human sense of smell using sensor arrays and pattern recognition systems.

Colorectal cancer is a highly treatable form of cancer if it is detected at an early stage. However, colonoscopies, which are currently considered the most effective way to detect colorectal cancer, can be invasive and uncomfortable, which may discourage some people from getting screened.

Having more early screening non-invasive alternatives such as breath testing may help encourage younger people who have an above-average risk of colorectal cancer but are not yet eligible for traditional screening methods. It is important for people who have a higher risk of colorectal cancer to get tested as early detection can potentially save lives.