A complex comprising a non-absorbable portion attached to an iron chelator moiety, a composition comprising the complex and the use of the complex in the treatment of colorectal cancer. In one embodiment the non-absorbable portion is a polymer such as a polysaccharide, including chitosan, chitin, cellulose or pectin. In one embodiment the iron chelator moiety comprises at least one functional group selected from catechol, hydroxamate or carboxylate, or any combination thereof.