Meral Nugent is understood to have taken a local authority PR job.
The RCR, which aims to ensure people get appropriate and timely cancer care, has around 6,600 members and fellows.
The body hit the headlines in Scotland last month when it expressed concern that the country's busiest cancer centre was using outdated equipment.
AS Biss consultant Dominic Pendry is co-ordinating media briefings and advising RCR spokespeople.
The agency's contract is likely to expire when the RCR has found a replacement for Nugent. Recruitment for the post is ongoing.