Cerium (Ce) - Calcium's Doppelganger

• a rare earth element (atomic number 58) that is actually more common than lead!
  
• the trivalent form of this metal resembles (divalent) calcium in size and things it likes to bind to, enabling it to mess with calcium-dependent physiological processes like blood clotting, muscle contraction, and neurotransmitter release.
• given their effects on blood clotting, a number of rare earth elements, including cerium, were considered for development into anticoagulants prior to the dawn of the age of heparin
• cerium salts, particularly cerium(III) oxalate, were used roughly between 1850 and 1950 to stop people from puking, but no one knows exactly how they accomplish this nor how effective they really are (there are no good papers on it)
  
• cerium salts are also capable of both inhibiting the growth of and actively killing bacteria
• the recognition of this ability in the late nineteenth century lead to their use as topical antiseptics (they had fun names like "dymal", "ceolat", and "ceriform"), an application which continues to this day (typically cerium nitrate as an adjunct to an antiseptic silver compound)
• the salts also appear to modulate the immune system in such a manner as to help burn victims resist sepsis (likely by inactivating burn toxins and other such endogenous immunosuppressive agents)
• perhaps most interestingly, a solution of cerium(III) iodide called "introcid" was injected into cancer patients during the early days of cancer chemotherapy and was found to shrink tumours more effectively than other iodine compounds, suggesting that it was the cerium and not the iodine that gave the cancer a beating
  
• cesium(III) complexes are reportedly being developed as cancer drugs, and are particularly exciting because they appear to take out multi-drug-resistant varieties of cancer just as easily as sensitive varieties
  
• since calcium is involved in the control of cell proliferation, the development of cancer cells, and angiogenesis, all components of tumour development, it is possible that cerium works as an anticancer agent because it can royally put the screw to these processes
  

Jakupec MA, Unfried P, Keppler BK. Pharmacological properties of cerium compounds. Rev Physiol Biochem Pharmacol. 2005;153:101-11. Review.