Disclosed is a composition for delivering a therapeutic or diagnostic agent to a disease site in a mammal comprising the therapeutic or diagnostic agent coupled to a Secreted Protein, Acidic, Rich in Cysteines (SPARC)-binding-polypeptide (SBP) and a pharmaceutically acceptable carrier, wherein the SBP comprises SEQ ID No 1. Further disclosed is a method for delivering a therapeutic or diagnostic agent to a disease site in a non-human mammal, and the use of a therapeutic agent coupled to a SBP that comprises SEQ ID No 1 in the manufacture of a medicament for treating a tumour.
