A method of treating cancer through use of guanosine 3′,5′-cyclic monophosphate (cyclic GMP). Cyclic GMP decreases the number of human breast cancer and prostate adenocarcinoma as well as small-cell and squamous lung cells in culture by 30% (1 μM), 84% (1 mM), 31% (1 μM), and 30% (1 μM), respectively. Cyclic GMP decreases DNA synthesis in human pancreatic, breast, and prostate adenocarcinomas as well as small-cell and squamous cell carcinomas of the lung at its 1 μM concentration by 51%, 54%, 56%, 50% and 52%, respectively. Cyclic GMP when infused for one week decreases the tumor volume of human pancreatic adenocarcinomas in athymic mice 95% compared to untreated animals with human pancreatic adenocarcinomas.
