Cancer Research UK will be "casting the net as wide as possible" in the search for a successor to chief executive Professor Alex Markham.
Markham will step down in spring 2007 to return to the University of Leeds, where he will take up the post of West Riding professor of medicine after a three and a half year secondment.
He joined Cancer Research UK in 2003, 18 months after it was formed by the merger of the Imperial Cancer Research Fund and the Cancer Research Campaign in 2002.
"We are all enormously grateful to Alex, who has done so much for the cancer community and for Cancer Research UK during his time as chief executive," said David Newbigging, the charity's chair. "We are sad to see him go."
Macmillan Cancer Support is also seeking a replacement for its chief executive, Peter Cardy, who leaves at the end of this month.
