A c-Myc antisense phosphorodiamidate morpholino oligomer (PMO) with potential antineoplastic activity. Phosphorodiamidate morpholino oligomer AVI-4126 binds to c-Myc mRNA and blocks its translation, which may result in the death of tumor cells overexpressing c-Myc. Differing from traditional antisense oligodeoxynucleotides (ODNs), neutrally charged PMOs are composed of subunits of nucleic acid bases linked to a synthetic backbone and, so, are less prone to enzymatic degradation. c-Myc, a proto-oncogene overexpressed in a variety of cancers, is involved in cellular proliferation, differentiation, and apoptosis.