The scientists studied how mass spectrometry, a technique for molecular-level characterisation of chemicals and biochemicals, can be used to analyse human breath to detect cancer. Recent studies have noted that dogs are able to identify with high confidence the presence of cancerous tissues in patients at an early stage, based on sniffing a breath sample. The EU-funded research 'Characterisation of biomarkers in breath of lung and breast cancer patients' (Breath) delved further into this idea by characterising biomarkers in the breath of lung and breast cancer patients. There are several highly compelling reasons for using the breath to analyse patients' health. The method is non-invasive, meaning less patient discomfort, and the process is quite fast, so the technique could be used for large-scale screening. Substantial literature already exists on breath analysis for medical diagnosis - indeed it is well known in metabolic, pharmaceutical and chemical research. But few clinical applications for mass-spectrometric diagnosis have resulted to date. As the technique becomes more common, better understood and more reliable, the number of potential applications should grow. In the meantime, more work is needed to accurately match the presence of biomarkers with particular diseases like breast cancer. That confidence is lacking because most mass spectrometers are not very good at analysing large bio-molecules typically found in the breath and other organs, for example. But the Breath research sought to overcome that problem by using a particular kind of mass spectrometry. Macro-molecules The basic principle of mass spectrometry combines an ion source to charge (or ionise) the material to be studied, a mass analyser, which sorts particles according to their mass, and finally a detector. It measures the number of each ion present. Once combined, the information provides a characterisation of a given sample. The Breath research sought to apply a relatively recent form of the technique, called 'Secondary electrospray ionisation MS' (SESI-MS). Electrospray was just revealed to the world in 1988 and as early as the mid-1990s it prompted the development of life-saving AIDS medications, called protease inhibitors. The key advantage of electrospray is how fast it can analyse complex pharmaceutical preparations - preparations consisting primarily of large biological, macro-molecules. These are exactly the type of molecules scientists need to identify in order to detect the presence of cancer, so Breath applied this technique to the problem at hand. SESI-MS was used to monitor the breath metabolites of a group of healthy subjects over several months, revealing that each person had their own characteristic 'breath signature'. This is important for metabolic studies because one of the major issues is the different sources of temporal variability caused by diet and other factors. That variability ultimately changes the metabolic fingerprint within a subject. In spite of this 'temporal noise', the researchers found a stable metabolic fingerprint which proved to be individual-specific. Once the technique was optimised, the researchers investigated the differences in the breath patterns of a group of lung- and breast cancer patients and healthy controls with the aim of identifying a set of metabolites over- or under expressed in cancer patients. This was motivated because several reports support the idea that dogs can identify cancer tissues based on their characteristic odour signature. New analytical instrument, too The European researchers also worked on a new approach to the statistical analysis of study samples, and validated the new method against traditional chemometric tools. During the exercise they could successfully discriminate between a group of colo-rectal cancer patients and healthy controls based on their plasma mass spectral fingerprint, another important output for the researchers. They also found that their system could identify and quantify free fatty acids, very important compounds involved in many metabolic processes. It means the SESI-MS system could have applications beyond cancer screening. The researchers explored the capabilities of a novel analytical instrument, called the differential mobility analyser, coupled with mass spectroscopy to analyse a prostate cancer biomarker. The main advantage of this technique is its analysis speed compared to traditional methods, which lends itself well to potential large-scale clinical practice, suggest the researchers. Breath received funding from the Health initiative of the EU's Seventh Framework Programme for research.