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Folate receptor 1 (FOLR1), also known as folate receptor alpha or adult folate-binding protein (FBP), is a 38-kDa glycoprotein belonging to the folate receptor family (PMID:15094207; 23528302). The receptor binds to folate and reduced folic acid derivatives and mediates delivery of 5-methyltetrahydrofolate to the interior of cells. FOLR1 is a secreted protein that either anchors to membranes via a glycosyl-phosphatidylinositol linkage or exists in a soluble form. FOLR1 expression is often limited to the apical surfaces of epithelium in the lung, kidney and choroid plexus but is differentially overexpressed in a variety of solid tumors such as ovarian cancer, non-small cell lung cancer, breast cancer, kidney cancer and high-grade osteosarcoma (PMID: 23528302; 23357463).