A small-molecule radiopharmaceutical consisting of the beta-emitting radioisotope iodine I 131 attached to a phospholipid ether (PLE) analogue, comprised of a linear 18 carbon backbone, with potential antineoplastic activity. Iodine I 131 phospholipid ether analogue CLR1404 selectively accumulates in tumor cells, thereby delivering a cytotoxic dose of radiation to cancer cells. Compared to normal cells, tumor cells are unable to metabolize and eliminate PLEs possibly due to deficiency of the enzyme phospholipase-D. In addition, the radioiodine moiety of this agent is resistant to de-iodination.