PSAT1 and breast neoplasm: By analyzing 297 ER-negative breast tumor samples and 112 non-cancerous samples by immunohistochemistry for PSAT1, positive staining (brown) was detected in the majority of ER-negative tumor tissues but was detected less frequently in non-cancerous tissues (Fig. 1e, f), indicating that protein expression of PSAT1 is elevated in ER-negative breast cancers compared with non-tumor tissues (p = 0.002).