methods of preventing and / or treating cancer are disclosed . the methods comprise administering to the patient a pharmaceutically effective amount of a water - soluble , acid - stable organometallic nanoparticles , optionally in combination with another therapeutic agent . in particular , nanoparticles that consist of polymerized citric acid and various different types of metals including , but not limited to , iron , calcium , zinc , silver and magnesium . these nanoparticles are acid - stability and self - degradation leading to constituent metal release when ph rises closer to the neutral ph of 7 or higher .