The novel diagnostic method for colorectal cancer: Detection of methyl mercaptan from flatus.

529 Background: Fecal occult blood test screening for colorectal cancer (CRC) reduces cancer specific mortality through the detection of early stage disease. However, medical examination rate is very low in Japan because of the inconvenience of sampling of stool. On the other hand, it is reported that dogs can be trained to distinguish breath samples of patients with lung and breast cancer from those of control. It is unclear that odour materials become effective tools in CRC screening. The aims of this study were to evaluate the gas components in the flatus of CRC patients and to compare with healthy controls. Methods: Thirty-two patient before elective colorectal surgery in Yokohama City University and 13 healthy controls were enrolled in this study.The apparatus for gas sampling was placed in the toilet. Defecation gas from a patient in a toilet stool was collected in a 25L sampling bag. A fan (50 L / min ) was arranged to aspirate air in the toilet stool. Defecation gas components were collected as follows: (1) Air in the toilet stool was aspirated with the fan and passed through a commercial gas sensor. (2) Gas sampling started after the gas sensor detecting gas components.Volatile sulfur-containing compounds in sampling bag were injected into the gas chromatography by Entech pre-concentrator and analyzed. Results: The amount of methyl mercaptan was significant higher compared with control. Methyl mercaptan and hydrogen sulfide were related to tumor size (r = 0.415，p = 0.018, r = 0.454，p = 0.009). Methyl mercaptan tended to increase as the stage advances (p = 0.022）．Based on an optimal cut-off value calculated by ROC curve analysis had accuracy, sensitivity, specificity, positive predictive value, and negative predictive value of 68.9%, 68.8%, 69.2%, 84.6%and 47.3%, respectively, for the diagnosis of CRC. Conclusions: The methyl mercaptan from the toilet stool during defecation was increasing in CRC patients. Measurements of methyl mercaptan suggests possibility of more easily and precise colorectal cancer screening.