TOP1 and gastric cancer: We found that a gene annotated in some genomes as an integrase was present in more than 80% of the genomes of H. pylori isolated from gastric cancer; the second gene found at high frequency was a DNA topoisomerase I. Both are encoded within a genomic island of the H. pylori 29CaP genome named ICEHptfs3 (Fischer et al., 2014).