FASN and neoplasm: Not only can tumor cells synthesize lipids by using some enzymes, including fatty acid synthase (FASN), sterol regulatory element-binding proteins (SREBPs), acetyl-coenzyme A (Ac CoA), stearoyl-CoA desaturase 1 (SCD1), acetylCoA carboxylase (ACC), but also they can absorb lipids directly from the external environment through different ways (45).