It plans to appoint another creative shop in addition to the three agencies that already handle its £1.5 million annual spend.
Carolan Davidge, the charity's brand and PR director, said: "We're looking for an agency that will build on our successful track record, deepen public understanding and engagement with us, and help support a challenging programme of income generation."
Cancer Research UK currently retains Rapp as its direct agency, while Ogilvy handles its breast cancer awareness assignment and MediaCom its media planning and buying.
The charity, which is al- most entirely funded by public donations, has a network of about 600 shops and 1,000 local fundraising groups. It supports research through the work of more than 4,250 scientists, doctors and nurses.