Letrozole (a non-steroidal aromatase inhibitor) also inhibited the growth of breast cancer cells by induced cell cycle arrest at the G0/G1 phase (but without G2/M arrest) and apoptosis by the intrinsic pathway, which was associated, among others, with the decreased Bcl-2 protein expression and the increased BAX protein expression. The gene discussed is CYP19A1; the disease is breast cancer.