Cancer cells are usually markedly different from normal cells in the body. These differences may relate to their rate of division, their structure, but also the production of various types of substances. The latter phenomenon was the basis for the work of London scientists, who decided to develop a non-invasive breath test to diagnose oesophageal and gastric cancers. According to the scientists, analysis of five substances in the air exhaled by patients could allow non-invasive diagnosis of cancer.