Estrogen receptor-negative/progesterone receptor-positive Evsa-T mammary tumor cells: a model for assessing the biological property of this peculiar phenotype of breast cancers

In 1986 we reported the appearance of a progestin binding protein in the human breast cancer cell line Evsa-T, originally described as lacking both estrogen and progesterone receptors (ER and PR). In this report we show that PR of this cell line displays a binding affinity for [3H]ORG 2058 and a sucrose gradient sedimentation profile similar to those ascribed to PR from MCF-7 or T47D breast cancer cell lines. PR from Evsa-T cells is down-regulated by the progestin R-5020 as well as by the two antiprogestins, ZK 112.993 and ZK 98.299, but does not confer growth sensitivity to these compounds. ER remains undetectable by ligand binding assay, enzyme immunoassay and northern blotting. Our Evsa-T clone could be a valuable model for assessing the mechanisms leading the ER−/PR+ phenotype occurring occasionally in breast cancers and frequently in meningiomas.