Abstract
Diagnosis of colorectal cancer is an invasive and expensive colonoscopy, which is usually carried out after a positive screening test. Unfortunately, existing screening tests lack specificity and sensitivity, hence many unnecessary colonoscopies are performed. Here we report on a potential new screening test for colorectal cancer based on the analysis of volatile organic compounds (VOCs) in the headspace of faecal samples. Faecal samples were obtained from subjects who had a positive faecal occult blood sample (FOBT). Subjects subsequently had colonoscopies performed to classify them into low risk (non-cancer) and high risk (colorectal cancer) groups. Volatile organic compounds were analysed by selected ion flow tube mass spectrometry (SIFT-MS) and then data were analysed using both univariate and multivariate statistical methods. Ions most likely from hydrogen sulphide, dimethyl sulphide and dimethyl disulphide are statistically significantly higher in samples from high risk rather than low risk subjects. Results using multivariate methods show that the test gives a correct classification of 75% with 78% specificity and 72% sensitivity on FOBT positive samples, offering a potentially effective alternative to FOBT.
Highlights
Colorectal cancer is the fourth most common cancer in men and the 3rd most common cancer in women
Inhibited by hydrogen sulphide non-competitively. This inhibition causes a reduction in cellular adenosine triphosphate (ATP) which subsequently has a direct effect on the ATP sensitive potassium channels
partial least squares discriminant analysis (PLS-DA) following feature selection with the Wilcoxon T test (WTT) produced a promising result with a classification accuracy of 75%, a specificity of 79%, and a sensitivity of 70%
Summary
Colorectal cancer is the fourth most common cancer in men and the 3rd most common cancer in women. There is significant international variation in the distribution of this cancer [1] and it is often regarded as a disease of Western industrialised countries. This strongly suggests that environmental factors may play a major role in the aetiology [2], and the highest incidence rates of colorectal cancer are located in North America, Europe and Oceania [1,3]. Despite the higher incidence of this cancer, mortality has been found to have decreased in 13 out of 29 countries [1]. The decrease is generally considered to be due to improvements in treatment, screening and earlier detection and was seen in longstanding economically stable.
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