MTOR (mechanistic target of rapamycin, FRAP1) is a serine/threonine protein kinase that acts as a central regulator of cellular metabolism, growth and survival in response to hormones, growth factors, nutrients, energy and stress signals. MTOR directly or indirectly regulates the phosphorylation of at least 800 proteins. Overexpression of MTOR is related to tumorigenesis in breast, lung, bladder, brain, renal, thyroid, and prostate cancer as well as melanoma and leiomyosarcoma, and it is a target of therapeutic inhibitors. In immunohistochemistry of normal tissue, MTOR has membranous and cytoplasmic positivity in epithelial tissues throughout the body including intestinal crypts, the isthmic region of the stomach, pancreatic ductal cells, liver bile ducts, the kidney distal nephron and the bladder. References: Dis Markers. 2017; 2017: 1397063, PMID: 28831205; Mod Pathol 2011;24:1553, PMID: 21822208; Mod Pathol 2012;25:197, PMID:22080063