Phosphoserine aminotransferase 1 (PSAT1) is coded by the PSAT1 gene at chromosome 9q21.2. It is a pivotal enzyme to produce serine and α-ketoglutarate, two critical metabolites for both carbon metabolism and the tricarboxylic acid cycle. PSAT1 is a rate limiting enzyme in the serine-glycine synthesis pathway which produces glycine, an essential nutrient for proliferating normal and neoplastic cells. Multiple studies have suggested that PSAT1 overexpression causes increased tumor cell proliferation, tumor progression, and poor patient prognosis in several different cancer types. Germ line PSAT1 mutations are among the causes for serine deficiency disorders which constitute inherited metabolic diseases with a broad phenotypic spectrum including the Neu–Laxova syndrome. In normal tissues, PSAT1 is mainly expressed in the brain, the kidney, and the pancreas but it also occurs in other cell types. Among tumors, PSAT1 expression is most often seen in brain, ovarian and endometrial carcinomas, although PSAT1 expression can also occur in tumors of various other organs.