Immunohistochemistry assays for enzymes of serine (and glycine) metabolism, including PHGDH, PSAT1, PSPH, and serine hydroxymethyltransferase, and surrogate markers for identification of molecular tumor type revealed that, among TNBC tumors, basal marker-positive patients exhibited increased expression of PHGDH relative to basal marker-negative patients (P = 0.029). Here, PSAT1 is linked to neoplasm.