Circular RNA (circRNA) is a special group of non-coding RNA which forms a covalently closed continuous loop from exon circularization. Recent studies have shown the role of circRNAs in cancer and increasing evidence points to their potential application as biomarkers in cancer. Recently, with the development of high throughput sequencing technology, a large number of circRNAs have been discovered across species. These circRNA molecules were found to be evolutionary conservative, stable, and specifically expressed across tissues or developmental stages. Therefore circular RNA has become the hotspots in the current transcriptomics research field. Circan provides an integrated circRNA database to benefit functional studies of cancer-specific circRNAs. It lists circRNAs associated with 20 major cancer subtypes. All the data, including circRNA name, parent gene, genomic coordinates, sample source, miRNAs associated with circRNAs were organized into a set of interactive MySQL tables. To bridge the large gap between the overwhelming number of circRNAs and their biological functions, we compiled this comprehensive repository of circRNAs.