As estimated by a radioligand binding assay (100 nM 3H-FA, 1 h at 37°C), the ranking order of total available FRs on these cell lines was: 9 × 104 (OV90, a low-FR expressing ovarian cancer cell line), 1.9 × 105 (THP1-FRβ), 2.4 × 105 (HOS-FRαfLuc), 7 × 105 (HOS-FRα), 2.1 × 106 (MDA-MB-231), and 4.8 × 106 (KB) FA molecules/cell. This evidence concerns the gene FOLR2 and ovarian carcinoma.