Since FAS is essential for tumor cells, for its growth and survival, and is upregulated and overexpressed in variety of tumors,[1] scientists have high expectations for FAS as an oncology drug target.[20] Orlistat inhibits FAS with the same mechanism as it does with pancreatic lipase, that is by binding covalently to the active serine site.[20] This effect of orlistat as a FAS-inhibitor was first identified in a high throughput screening for enzymes with prostate cancer inhibition activity.