It wasn't that long ago that genetic mutation and genomic instability were the only mechanisms known to alter gene expression in cancer. However, over the past few years, it has become increasingly evident that DNA hypermethylation — especially at the promoters of key tumour-suppressor genes — is another mechanism by which genes can be silenced in cancer. But the relationship between DNA methylation and cancer is not a simple one — genome-wide hypomethylation is also a feature of cancer-cell genomes, and it remains unclear whether DNA hypermethylation is the initial switch that silences genes in cancer cells or maintains their silenced state. On p415, Stephen Baylin and Peter Jones discuss new insights into these and other questions about the role of DNA methylation in cancer that have come from recent studies in both their field and that of chromatin remodelling, which are beginning to link the events that lead to the formation of transcriptionally repressive chromatin to DNA methylation. The reversibility of this gene-silencing process — unlike gene silencing by genetic mutation — means that this field of research holds much promise for the future treatment of cancer.

You'll also find two new additions to the journal in this issue — a new feature in Highlights called Ethics Watch and the publication of our first piece of online correspondence (see p487 and the January issue table of contents online). The Ethics Watch column — written each month by an invited contributor — has been introduced to give ethics a more timely and regular presence in the journal and to bring to you the opinions of those who are actively involved in tackling ethical issues raised by genetics research. The online correspondence is there to give you, the reader, the opportunity to comment on any aspect of the scientific content of the journal.