Phillip Dennis of the National Cancer Institute and his colleagues exposed normal human lung cells to concentrations of nicotine and its derivative NKK comparable to those supplied by cigarettes. Within minutes, the team found, the so-called Akt molecular pathway became active. This pathway fosters cell growth and survival and is thus antithetical to the body's major defense against cancerous tumors: apoptosis, or programmed cell death. The researchers also identified active Akt pathways in the lungs of mice treated with NKK and in the lung tissue of smokers. The authors conclude that although nicotine is not yet considered a carcinogen, their findings might have implications for smoking cessation methods because "the risks of long-term nicotine supplementation are unknown."