In a further related aspect, the invention is a purified and/or synthetic thrombospondin fragment or portion thereof, said fragment being one that starts between amino acid I-165 (just after the N12/I peptide) and V-263 (the start of the procollagen homology domain), inclusive, and ends between amino acid I-530 (the end of the type 1 repeats) and R-733 (the end of the first type 3 repeat), inclusi