Non-coding RNAs have recently been identified as important regulatory elements in mammalian and non-mammalian cells. In human cells, the number of microRNAs has been expected to exceed the one thousand mark. In cancer research, the interest in this class of small RNA molecules is particularly pronounced. This originates from aberrant expression patterns of specific microRNAs in various forms of human cancers as well as from proposals that specific microRNAs contribute to oncogenesis by either fulfilling tumorsuppressor functions or acting themselves as oncogenic factors. The expression profiles of microRNAs seem to vary in different types of presently analyzed human cancers, although characteristic patterns have been established for specific types of carcinomas.

Besides their role in basic mechanisms leading to oncogenesis, they already start to play an increasing role in the diagnosis, prognosis and response to treatment of cancer patients. It is somewhat likely that their role will be extended in the future to therapeutic approaches, in particular to the identification of new therapeutic targets.

The International Journal of Cancer wishes to emphasize the importance of this rapidly evolving field . The “Special Section” of this issue presents two contributions from pioneers in this field, George Calin from the MD Anderson Cancer Center in Houston, Texas, and Lin Zhang, Department of Obstetrics, University of Pennsylvania, Philadelphia, and their respective co-workers. The report by the Calin group emphasizes the role of miRNA profiling as diagnostic tools, whereas Zheng and colleagues stress the characterization of epigenetic regulation of microRNA as potential cancer biomarkers and as new therapeutic targets for future development.

Jointly with my co-organizer of this Special Section, Webster Cavenee, I wish to express our gratitude to both groups for their contributions and trust that the International Journal of Cancer will provide a forum for future contributions in this exciting area of cancer research.