NNK also induces cancer cell proliferation through engaging various signal transduction molecules and transcription factors, including ERK1/2 MAPK, p38 MAPK, PI3K/AKT, NF-󠇯κB, cyclooxygenase-2 (COX-2), B-cell lymphoma 2 (Bcl2) and c-Myc [79,80,81,82,83,84] (Figure 2). This evidence concerns the gene PTGS2 and cancer.