MAOA and cancer: In cancer cell lines (Ca9-22), compared with the untreated control group, mRNA expression of MAO-A was increased slightly at 50 μM. Conversely, a greater than 2-fold change in the downregulation of MAO-A was found to be statistically significant at 100, 200, 400, and 800 μM arecoline treatments compared with the control group (0 μM) (P < 0.05); the change in downregulation was particularly significant at 800 μM arecoline in the Ca9-22 cancer cell line (the mean fold change ± standard errors (SE) was −8.55 ± 0.33).