The present invention is directed to peptides having affinity for tumor cells. The peptides are useful in pharmaceutical compositions in particular for the treatment of cancer. Further, the peptides are useful in diagnostic compositions, in particular for the diagnosis and imaging of cancer. The peptides according to the present invention are peptides selected from the group consisting of: Z1-KLAKLAKKLAKLAK-Z2-LTVXPWY-Z3, Z1-KLAKLAKKLAKLAK-Z2-LTVXP-Z3, Z1-KLAKLAKKLAKLAK-Z2-TVXPW-Z3, Z1-KLAKLAKKLAKLAK-Z2-VXPWY-Z3, Z1-KLAKLAKKLA KLAK-Z2-XPWY-Z3, Z1-KLAKLAKKLAKLAK-Z2-LTVXPW-Z3, di-, tri-, or multimers of the above sequences, wherein each Z1, Z2 and Z3 independently of one another represents any amino acid sequence of n amino acids, n varying from 0 to 50 and n being identical or different in Z1, Z2, and Z3, and wherein X represents any amino acid, whereby each of the amino acid residues in the above sequences may be independently in either L-form or D-form.
