Nature Milestones are special supplements that aim to highlight the 'Milestones' or remarkable achievements in a given field. Each Milestone is covered in a short article, written by editors from the Nature Publishing Group, which discusses landmark discoveries in the context of the prevailing concepts at the time, and our current knowledge of the field.

Milestones in Cancer − the fourth supplement in a series that also includes Milestones in Cell Division, Milestones in Development and Milestones in Gene Expression − covers the historic discoveries made in this area since the end of the nineteenth century. This issue is a collaboration between three Nature Publishing Group journals: Nature, Nature Medicine and Nature Reviews Cancer.

Cancer research is an extremely broad topic, and we have focused on the basic biological mechanisms underlying tumour development rather than on clinical aspects. The Milestones covered here were chosen in collaboration with a panel of more than 40 advisors who provided a list of important discoveries and papers in their fields, and had input into the Milestone articles. Although we have attempted to be comprehensive and to cover those discoveries viewed by the community as most significant, there will no doubt be omissions.

Key scientific discoveries are, for the most part, not achieved in single discrete steps, and involve the work of many investigators, and the fusion of ideas, models, experimental evidence and general acceptance based on a body of work. These articles are therefore by no means intended to be a comprehensive coverage of a particular discovery, but instead aim to highlight the main papers and to convey a historical perspective on how a given concept evolved.

In addition to the Milestone articles, the supplement includes a Timeline, which is a chronology of the earliest papers for each Milestone, and a collection of selected Reviews and Perspectives from the participating journals.

The Milestones web site also includes advisors' biographies and a Nature Publishing Group library containing relevant content from the participating titles. The content of the supplement, as well as selected Research and Review articles from the Nature Publishing Group library, will be available freely until 30 September 2006. We hope that Milestones in Cancer will be an enriching reflection on the history of this field.

Finally, we would like to extend our sincere thanks to the advisors and to acknowledge support from our sponsors: Applied Biosystems, AstraZeneca, Genentech, Cancer Research UK and Imclone Systems Incorporated. As always, Nature Publishing Group takes complete responsibility for the editorial content.