The need for monitoring the actual nitric oxide concentration in tumors.

The significance of the role of nitric oxide (NO) in cancer is evident from 1,100 publications on the subject; its triggering of apoptosis at high concentrations is documented in 300 publications. While aspects of the rate of generation of NO in tumors have been extensively studied, the rate of its removal from tumors has not been considered, even though it is the difference between the two rates that determines the all important steady-state NO concentration, and thus the likelihood of apoptosis-triggering. The rate of transport of NO scales with its concentration gradient at the interface between a neoplasm and the phase to which it diffuses, which can be air, fat, or blood. Diffusional loss of NO to air would explain the initial two-dimensionality of neoplasms of the skin and lung. The greater solubility of NO in lipids than in aqueous phases should cause its extraction by nearby fat, and would account for the positive correlation between obesity and the incidence of some cancers, such as cancers of the breast. And the rapid consumption of NO by red blood cells implies depletion of excess NO in tumors after they are vascularized: angiogenesis should blunt any apoptosis-triggering NO attack of the immune system. Thus, cancer research and the practice of oncology may benefit of in-tumor monitoring of the actual NO concentration. Miniature NO monitoring electrodes, that might serve the purpose, are reviewed.