NNMT and cancer: We and other groups have reported that 1‐MNA, one of the metabolites generated from N‐methyltransferase reaction of NNMT, somehow demonstrated cancer‐promoting effect and immune regulatory effect under different scenarios.[21, 30] To investigate the contribution of 1‐MNA to breast cancer progression, we stimulated NNMT‐absent SKBR3 cells with 1‐MNA and test its effect on cell‐cycle progression.