PSAT1 and cancer: Interestingly, in the same paper it has been shown that stromal cells in brain metastasis overexpress the SSP enzymes PHGDH, phosphoserine aminotransferase (PSAT), and phosphoserine phosphatase (PSP) as well as SHMT1, suggesting that an increased amount of serine and glycine could be produced and released by the stroma to support cancer cells [44].