Nitric oxide concentrations in tumors do not reach apoptosis inducing levels when their excess NO is rapidly depleted. The out-flux of NO from a tumor to air or blood scales with the contacting area and with the concentration gradient; the gradient scales with the tumor-air or tumor-blood concentration difference and scales inversely with the thickness of the boundary layer, i.e. the fluid's flow rate. Air-contacting skin and lung cancers account for approximately 60% of all cancers in part because out-diffusion of NO from nascent tumors to air increases the likelihood of their survival. Out-diffusion of NO also explains their initially 2-D spreading at the air interface. Blood is an NO sink because its proteins are rapidly S-nitrosated; depletion of NO by the blood explains the dormancy of tumors until their vascularization and their virulence after vascularization. Erythrocytes store NO(2)- and their carbonic anhydrase converts it to NO and NO(3)(-). Thus, NaNO(2), a common additive in cured meats, may reduce NO out-diffusion by raising the blood NO concentration.