Tributes have been flooding in for Margaret Hamburg after she confirmed that she is stepping down as commissioner of the US Food and Drug Administration.

Ms Hamburg, who has held the role for nearly six years, said in a letter to FDA staff that her time at the head of the agency has been "the most rewarding of my career” and a "privilege”. She noted that “this decision was not easy” and “while there is still work ahead (and there always will be), I know that I am leaving the agency well-positioned to fulfill its responsibilities to the American public with great success”.

FDA chief scientist Stephen Ostroff will serve as acting commissioner, while Robert Califf, recently picked to become the agency's deputy commissioner for medical products and tobacco, is being touted as Dr Hamburg’s successor.

US health secretary Sylvia Burwell praised Dr Hamburg for her "dedicated service”, saying her achievements at the helm were "incredible" and "historic”. Richard Schilsky, chief medical officer of the American Society of Clinical Oncology (ASCO) said that under her leadership, “we have made great strides in cancer treatment and in how we implement precision medicine”.

He added that Dr Hamburg “has been at the forefront of ensuring that the FDA is keeping pace with this rapid scientific change and using available mechanisms to speed patient access to safe and effective therapies”.