SHMT2 and breast cancer: An upregulation of SSP enzymes in hypoxia has previously been found in breast cancer cells.41 In line with that, hypoxia led to an upregulation of SHMT2 and PHGDH expression in MDA-MB-231 und MDA-MB-468 cells while SHMT1 expression was not induced or even reduced under hypoxia (Suppl.