Mechanistically, two FAO enzymes, medium-chain acyl-CoA dehydrogenase (MCAD) and long-chain acyl-CoA dehydrogenase (LCAD), reduce ROS levels to promote tumor cell proliferation, and loss-of-function of LCAD further accelerates cancer progression via involving in phosphatase and tensin homolog (PTEN) pathway [209]. The gene discussed is PTEN; the disease is neoplasm.