A protein binding to the extracellular domain B (ED-B) of fibronectin comprising the amino acid sequence of SEQ ID NO: 2, or a variant thereof having at least 90% sequence identity to SEQ ID NO: 2, wherein the ED-B binding protein or variant thereof has (i) a histidine at the position corresponding to position 6 of the wild-type sequence of SEQ ID NO: 32; (ii) an aspartic acid, arginine, threonine, or tryptophan at the position corresponding to position 8 of SEQ ID NO: 32; (iii) a glutamine, or proline at the position corresponding to position 38 of SEQ ID NO: 32; (iv) an aspartic acid, alanine, glutamine, asparagine, or a deletion at the position corresponding to position 62 of SEQ ID NO: 32; (v) a proline, histidine, lysine, glycine, tryptophan, or a deletion at the position corresponding to position 63 of SEQ ID NO: 32; (vi) a glutamine, lysine, or valine at the position corresponding to position 64 of SEQ ID NO: 32; (vii) a leucine, lysine, proline, serine, or arginine at the position corresponding to position 65 of SEQ ID NO: 32; (viii) a lysine, glutamine, histidine, or methionine at the position corresponding to position 66 of SEQ ID NO: 32; (ix) a threonine, glutamine, methionine, or leucine at the position corresponding to position 85 of SEQ ID NO: 32; (x) a glutamine, methionine, arginine, or tryptophan at the position corresponding to position 87 of SEQ ID NO: 32; (xi) a deletion at the position corresponding to position 141 of SEQ ID NO: 32; (xii) an aspartic acid at the position corresponding to position 142 of SEQ ID NO: 32; (xiii) a tyrosine, tryptophan, or alanine at the position corresponding to position 143 of SEQ ID NO: 32; (xiv) an arginine at the position corresponding to position 144 of SEQ ID NO: 32; and (xv) a phenylalanine, tryptophan, or tyrosine at the position corresponding to position 145 of the wild-type sequence of SEQ ID NO: 32; and wherein the ED-B binding protein or variant thereof has a binding affinity to the extracellular domain B of fibronectin of 10 nM or less in serum after incubation for at least 20 h. (i) a histidine at the position corresponding to position 6 of the wild-type sequence of SEQ ID NO: 32; (ii) an aspartic acid, arginine, threonine, or tryptophan at the position corresponding to position 8 of SEQ ID NO: 32; (iii) a glutamine, or proline at the position corresponding to position 38 of SEQ ID NO: 32; (iv) an aspartic acid, alanine, glutamine, asparagine, or a deletion at the position corresponding to position 62 of SEQ ID NO: 32; (v) a proline, histidine, lysine, glycine, tryptophan, or a deletion at the position corresponding to position 63 of SEQ ID NO: 32; (vi) a glutamine, lysine, or valine at the position corresponding to position 64 of SEQ ID NO: 32; (vii) a leucine, lysine, proline, serine, or arginine at the position corresponding to position 65 of SEQ ID NO: 32; (viii) a lysine, glutamine, histidine, or methionine at the position corresponding to position 66 of SEQ ID NO: 32; (ix) a threonine, glutamine, methionine, or leucine at the position corresponding to position 85 of SEQ ID NO: 32; (x) a glutamine, methionine, arginine, or tryptophan at the position corresponding to position 87 of SEQ ID NO: 32; (xi) a deletion at the position corresponding to position 141 of SEQ ID NO: 32; (xii) an aspartic acid at the position corresponding to position 142 of SEQ ID NO: 32; (xiii) a tyrosine, tryptophan, or alanine at the position corresponding to position 143 of SEQ ID NO: 32; (xiv) an arginine at the position corresponding to position 144 of SEQ ID NO: 32; and (xv) a phenylalanine, tryptophan, or tyrosine at the position corresponding to position 145 of the wild-type sequence of SEQ ID NO: 32;