CHEK2 and cancer: Some studies reported increased cellular proliferation and the inhibition of apoptosis in oral keratinocytes, while others found that arecoline promoted apoptosis and cell-cycle arrest in the G1/S phase and reduced cellular proliferation in SAS cancer cells and epithelial cells, as well as increasing the expression of ADHFE1 and ALDH1A2, and increased the phosphorylation of Chk1 and Chk2 [26,32,39,40,41,42].