A number of databases have been set up over the years to collect and organize several types of information related to cancer, such as somatic mutations of cancer genes (14), experimental evidence for their involvement in cancer (15,16) or modifications in gene expression levels (17,18). Other databases are specialized on particular types of cancer (19,20), on single genes (21,22) or on specific genomic modifications (23,24). None of the available resources, however, focuses on properties of cancer genes that are not strictly dependent on their function, but that could help in interpreting cancer as a ‘systems disease’. Here, we present the Network of Cancer Genes (NCG, http://bio.ifom-ieo-campus.it/ncg), a database that stores information on systems-level properties of a comprehensive dataset of more than 730 cancer genes. The collected features are duplicability, evolutionary appearance and topological properties in the human protein–protein interaction network. Protein interactions have been successfully used to infer functional links between proteins (25). In NCG, they are used to understand how the topological properties of the cancer proteins inside the protein–protein interaction network influence their role in cancer. NCG can
