ELISA assays showed that endogenous PPARγ ligands, 15(S)-HETE and 13(S)-HODE, were markedly decreased in NNK-treated tumor tissues (p = 0.0004 and p = 0.0035, respectively) and in human lung cancer samples (p = 0.011 and p = 0.022, respectively). This evidence concerns the gene PPARG and neoplasm.