Hanover will continue working on the six-figure account, having beaten four other agencies in the final pitch process for a brief that attracted 30 respondents.
The retainer brief will run until the end of 2013, and was one of the last to be dealt with through the COI. The work includes running the press office and production of publications.
Mark Saxon, who heads Hanover's healthcare division, will be leading the account.
He will report to Julietta Patnick, director of NHS Cancer Screening Programmes for England.
Hanover originally won the brief in 2007. The account covers breast, cervical and bowel cancer screening.
The agency's recent work includes managing the response to the late Jade Goody's battle with cervical cancer and the age-limit review that followed.
Saxon said: 'We've had a big focus recently in trying to reach key stakeholders, such as relevant cancer charities, communities and BME groups, as uptake has been low among the BME community.
'It's really important work and we are looking forward to continuing the programmes.'