The gut microbiota can be involved in the development of colorectal and liver cancer. The unveiling of the underlying processes provides promising starting points for creating novel diagnostic and therapeutic measures. This was demonstrated by the findings Prof. Robert F. Schwabe (Columbia University, New York, USA) and Dr. Peer Bork (University of Heidelberg, Germany) presented at the Gut Microbiota for Health World Summit in Barcelona (March 14-15, 2015).