Progesterone Receptor Antagonists – A Novel Treatment for Severe Hyponatremia from the Endocrine Paraneoplastic Syndrome

Abstract

Hyponatremia related to ectopic secretion of cancer cells of argininevasopressin (AVP) or atrial natriuretic peptide (ANP) is most commonlycaused by small cell lung cancer. The ideal treatment would be one thatnot only corrects the hyponatremia, especially if it is life threatening, butat the same time causes regression of the cancer, and thus improves bothquality and length of life. As one is waiting for chemotherapy, surgery,or radiotherapy to decrease the cancer burden, tolvaptan has been usedto correct the hyponatremia to improve symptoms or prevent death.Mifepristone, a progesterone receptor modulator/antagonist has been usedto treat various cancers. The oral 200mg tablet was given to an 80-year-oldwoman who developed sudden extensive lung cancer with a serum sodiumof 118 mmol/L. She refused chemotherapy but agreed to take mifepristone.The hyponatremia was completely corrected (145 mmol/L) within onemonth of treatment. She was in complete remission for 5 years and diednot from lung cancer, but an acute myocardial infarction. Mifepristonemay serve the purpose to not only quickly correct hyponatremia when itis related to an endocrine paraneoplastic syndrome, but also to provideimproved quality and length of life.