A composition of phosphodiester oligonucleotides of various defined sizes has been created that mimics the effects of defibrotide. The composition essentially consists of mixtures of synthetic phosphodiester oligonucleotides comprising Nmers ranging from 40 mers to 65 mers. The phosphodiester oligonucleotides are preferably heteropolymers composed of either A, G, C, and T at each position but may also be homopolymers, i.e. the same base may be present at each position in the oligonucleotide. These mixtures are effective in the treatment of cancer and other diseases.
