The Cyranose / Enose VOC testing with the eNose allows groups of patients to be tested for differences or similarities of breath signal . A single expired breath is collected in a sample bag then a pump draws the sample into the device where it passes over 32 electronic sensors. Over 400 possible chemicals affect these sensors in different ways, ad a pattern of electronic signals is generated. It is the distribution of the electric signals across the 32 sensors which gives the pattern. Software within the device determines which of the 32 sensors is giving the strongest signal in each test, and uses these sensor results in a combination result called a factor. This is known as Principal Component analysis. When comparing 3 groups of patients the software will generate 2 factors for each breath sample and plot these on a graph. Where a group of patients has a distinctive signal the factor analysis will clump that group together, at a certain "distance" on the graph from the other group. The greater the distance t(Mahalobinus distance) the more different the groups are. Numerous authors have published data on this type of analysis for a variety of disease states, particularly lung cancer. This approach is very easy technically and leads to further study of the individual VOCs which are responsible for the signal. It is likely however based on results from other tumours that a combination of VOCs are present in different amounts in cancer patients as opposed to a single VOC. The ENose approach has not been applied in Head and Neck cancer patients and nor has there been any report of detection of in situ cancer.